The increased incidence of ALS in military veterans of the first Persian Gulf War raised speculation that they may have a 'Persian Gulf' variant of ALS with atypical clinical features. Medical records of military veterans with ALS, previously identified in our epidemiological study, were evaluated for clinical features (age and site of onset, race, unexplained atypical findings) and ventilator-free survival. Comparisons between deployed versus non-deployed cohorts were made with deployment status based on designation by the Department of Defense Manpower Data Center (DMDC) or by self-report. Other than the young age of onset in both cohorts (40.8 years overall mean; 40.1 years for DMDC deployed, 41.2 years for DMDC non-deployed), review of the medical records failed to document any atypical features. After adjusting for bulbar onset, median survival from symptom onset in those > or =40 years of age was 35.5 months (2.96 years) compared to 64.7 months (5.39 years) in the group <40 years of age (hazard ratio (HR)=0.47, 95% CI 0.30-0.73, p=0.0006). After adjusting for age, median survival was 45.4 months (3.78 years) and 54.8 months (4.57 years) in bulbar- versus non-bulbar onset groups, respectively (HR=1.41, 95% CI 0.83-2.39, p=0.20). After adjusting for age and site of onset, deployed veterans had significantly shorter survival than non-deployed (40.2 vs. 57.0 months, HR=0.62, 95% CI 0.40-0.96, p=0.03) using DMDC data. In conclusion, although veterans developing ALS after deployment to the Persian Gulf in 1990-1991 exhibited otherwise typical clinical features, they experienced shorter ventilator-free survival than non-deployed veterans.