ALS is most common in Europe, North America, and parts of East Asia, with the highest reported rates appearing in Scandinavia, the United Kingdom, Italy, Japan, and the United States. Globally, incidence ranges dramatically, from as low as 0.26 per 100,000 people per year in Ecuador to 23.46 per 100,000 in certain regions of Japan. Where you live, your age, your sex, and even your occupation all influence your likelihood of developing the disease.
Countries and Regions With the Highest Rates
Europe consistently reports some of the highest ALS incidence in the world. Denmark leads at 5.55 per 100,000 person-years, followed closely by Scotland and Austria. Prevalence across the continent ranges from 3.44 per 100,000 in Malta to 10.80 per 100,000 in Italy. These numbers partly reflect better diagnostic infrastructure and more thorough case registries, but they also point to genuine geographic variation that researchers are still working to explain.
In North America, the overall incidence is about 1.44 per 100,000, based on CDC data covering 2012 to 2019. Prevalence in the United States reaches as high as 11.80 per 100,000, the highest point estimate reported in any country. Within the U.S., rates are not uniform. Vermont had the highest state-level incidence at 2.25 per 100,000, while Alaska had the lowest at 0.65. New England and the upper Midwest consistently showed rates above the national average.
Japan stands out in Asia, with a national incidence of 2.20 per 100,000, well above rates in other Asian countries like Iran (0.42) or China. But Japan also contains extreme local hotspots, which are discussed below. South America generally has lower rates, though Argentina reports an incidence of 3.17 per 100,000, comparable to many European nations. New Zealand reports 2.90 per 100,000.
Historic Hotspots: Guam and Japan’s Kii Peninsula
Two geographic clusters have fascinated ALS researchers for decades. In the 1960s and 1970s, the Chamorro people of Guam developed ALS at rates more than 100 times greater than anywhere else in the world. In certain villages, the rate was nearly 1,000 times the global average. A U.S. Navy doctor first noticed the pattern in 1945, when an unusual number of ALS cases appeared at the civilian hospital on the island.
Over the following decades, ALS on Guam slowly disappeared. Today, virtually no new cases occur among the Chamorro. This dramatic rise and fall strongly suggests an environmental trigger that was eventually removed or reduced, though no one has definitively identified what it was. Researchers have investigated everything from dietary habits to local water sources, but no single explanation has been confirmed.
A nearly identical pattern appeared on Japan’s Kii Peninsula, where ALS rates reached 6.42 per 100,000, and on the nearby island of Oshima, where the rate hit an extraordinary 23.46 per 100,000. Brain tissue from patients in both Guam and the Kii Peninsula shows strikingly similar abnormal protein deposits, suggesting a shared disease mechanism despite the thousands of miles between the two populations.
Who Gets ALS: Age, Sex, and Genetics
ALS is not evenly distributed across demographic groups. It is roughly 25% more common in men than in women, with a male-to-female ratio of about 1.25 to 1. That gap is driven almost entirely by sporadic ALS (the type with no family history), where the ratio rises to 1.29. In familial ALS, which accounts for about 5 to 10% of cases, the ratio is essentially 1 to 1.
The sex difference is most pronounced in younger adults. In one UK study, men under the typical age of menopause were 3.7 times more likely to develop ALS than women in the same age range. By older ages, the ratio narrows to around 1.2 to 1.4, which has led researchers to hypothesize that female hormones may offer some protective effect earlier in life.
Average age of onset is 56 to 58 for sporadic cases and about 52 for familial cases. The lifetime risk, adjusted for the possibility of dying from other causes first, is roughly 1 in 347 for men and 1 in 436 for women. If you have a first-degree relative with ALS whose genetic status is unknown, your lifetime risk rises to about 1.4%.
Environmental and Occupational Risk Factors
The geographic variation in ALS rates points strongly toward environmental influences layered on top of genetic susceptibility. Exposure to lead, pesticides, and agricultural environments have all been linked to increased risk, as have smoking and repeated physical trauma. One longstanding theory centers on a neurotoxic compound called BMAA, produced by cyanobacteria (blue-green algae) found in lakes, oceans, and soil worldwide. Some researchers believe chronic exposure to BMAA could help explain clusters like Guam and the Kii Peninsula, though this remains unproven.
Military service is one of the better-documented risk factors. A large prospective study found that men who served in the military had a 53% higher rate of ALS death compared to men who never served. After adjusting for age and smoking, the increased risk rose to 58%. This elevated risk was consistent regardless of whether the veteran served in World War II, Korea, or Vietnam, suggesting the link is not tied to a single conflict or specific chemical exposure like Agent Orange. The U.S. Department of Veterans Affairs recognizes ALS as a service-connected disease for all veterans with 90 or more days of active duty.
Why Rates Vary So Much by Location
Part of the global variation in ALS rates is real, and part is an artifact of how well different countries detect and record cases. Countries with robust neurology networks, national registries, and accessible healthcare naturally report higher numbers because fewer cases go undiagnosed. This is one reason Europe and North America dominate the top of incidence tables, while rates in sub-Saharan Africa and South Asia appear extremely low.
But detection bias does not explain everything. Even within well-surveyed populations, significant regional differences persist. The higher rates in New England and the upper Midwest compared to the rest of the U.S., for instance, cannot be attributed to differences in healthcare access alone. Researchers are actively investigating whether local environmental exposures, occupational patterns, or population genetics account for these clusters. The broad scientific consensus is that ALS results from gene-environment interactions, meaning that some people carry genetic vulnerabilities that only manifest when triggered by specific environmental conditions. Identifying those conditions is one of the central challenges of ALS research today.