We previously found an increased risk for ALS in Italian professional soccer players actively engaged between 1970 and 2001 (n =7325). The present study extends previous work with a prospective follow-up of the original cohort to 2006 and investigates the risk of ALS in two other cohorts of professional athletes, basketball players (n =1973) and road cyclists (n =1701). Standardized morbidity ratios (SMRs) were calculated. Among soccer players three new cases of ALS were identified, reaching a total of eight ALS cases (mean age of onset, 41.6 years). The number of expected cases was 1.24, with an SMR of 6.45 (95% CI 2.78-12.70; p<0.00001). The risk of ALS was higher for careers lasting >5 years, for midfielders, and for players engaged after 1980. No basketball player and no cyclist developed ALS. This prospective extension of the Italian soccer players cohort survey confirms the highly significant risk of developing ALS, the young age of onset, the dose-effect risk and a predilection for midfielders. The absence of ALS cases in professional road cyclists and basketball players indicates that ALS is not related to physical activity per se.