This investigation was conducted to clarify the epidemiology of ALS disease in Sardinia. During the years 1965-1974, the average annual incidence was found to be 0.64/100,000 inhabitants. On prevalence day, October 24th, 1974, the prevalence rate was 1.56/100,000 inhabitants. A significant male predominance was found, the average annual incidence rates for men and women being 0.88 and 0.40, respectively. The peak in both sexes was reached between 60 and 69 years. ALS distribution in the study area was uniform but its occurrence was significantly higher among agricultural workers (5.28/100,000). ALS started on average at 56.58 years and its duration was 2.5 years, being significantly longer in patients under 40-years-old. The distribution of the various clinical forms was: 66 per cent conventional forms, 20 percent bulbar and 14 per cent pseudo-polyneuritic. In the bulbar type, a female predominance was found. About 96 percent of cases were sporadic and 4 per cent familial. Familial cases presented no difference from sporadic cases. Trauma was present in 10.5 percent of the cases and gastrointestinal disfunction in 13 per cent. This probably reflects some relationship between trauma and ALS, and between malnutrition and ALS. No combination of ALS, dementia and parkinsonism was observed. Dementia was associated with ALS in four cases and Parkinson's disease in one case, separately. The combination of other disease states with ALS in the present study may be simple coincidence.