After World War II the southeastern part of Finland was ceded to the Soviet Union and its entire population evacuated to other areas of the country. The prevalences of amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) were studied among the evacuees and compared to the corresponding data among the nonevacuated population. The prevalence of ALS among the war evacuees was two times higher than among the nonevacuated population (18.0 and 8.8 per 100,000, respectively). The prevalence of MS among the evacuees was only half of that found among the nonevacuated population, 38.3 and 73.0 per 100,000, respectively. The findings for ALS indicate that birthplace may have an effect on the later development of the disease and that there may have existed some environmental factor(s) which have made the evacuees more liable to contract the disease later in their lives. The low figure of MS for evacuees supports our previous results of an uneven geographic distribution of MS in Finland with the high-risk areas in the western and southwestern parts of the country. No accumulation of MS was found among the evacuees living in the high-risk areas.