Our objective was to investigate incidence of amyotrophic lateral sclerosis (ALS) in Sicily, southern Italy, by means of a population based study. We included people with ALS resident in fi ve Sicilian provinces, whose onset occurred in the two-year period 2005 2006 (population at 31 December 2006: 3,481,096 inhabitants). A multisource case-fi nding procedure was adopted and patients were classifi ed as affected by ALS according to revised El Escorial criteria. During the two-year surveillance period, 97 patients meeting eligibility criteria included 57 males (58.8%) and 40 females (41.2%). Crude annual incidence rate was 1.4/100,000 person years (95% CI 1.33 1.47). The incidence rate was higher in males (1.71/100,000; CI 1.61 1.81) than in females (1.11/100,000; CI 1.01 1.21). Standardized incidence rate for the total population in the 45 74-years-old age group was 3.22 (CI 3.11 3.33). Prevalence rate was 6.0/100,000 (CI 5.97 6.03), higher in males (7.1/100,000; CI 7.02 7.18) than females (4.9/100,000; CI 4.86 4.94). In conclusion, ALS rates observed in the present study are higher in males than females, with a peak of incidence at 70 years of age in both genders. These fi ndings are consistent with those of other population based European studies