Sleep-related breathing events in patients with amyotrophic lateral sclerosis (ALS) have been reported in small case series, but the association with the clinical presentation--with (B) or without (nonB) bulbar symptoms--or the relevance for prognosis have not been investigated. We retrospectively analyzed sleep studies of 114 (46 nonB) ALS patients, aged 54 +/- 11 years. Respiratory function was better in nonB patients: forced vital capacity was 76 +/- 20% vs 55 +/- 23% in the bulbar group (p < 0.001); PaCO2 41 +/- 5 vs 44 +/- 6 mm Hg p < 0.05. The mean apnea/hypopnea index (AHI) was higher in nonB patients (22 +/- 12 vs 15 +/- 16 events per hour- p < 0.05); in this group 21 out of 46 patients (46%) had more than 20 events/hour versus 14 out of 68 (21%) in the nonB group (p < 0.005). On the contrary the oxygen desaturation index (ODI) was similar (10 +/- 11 vs 9 +/- 12 events per hour, p = NS). Most events had a central genesis and obstructive events were usually erratic, except in 7 patients (6 in group B) who had more than 10 obstructive events/hour. Data were stratified in three groups: with a disease duration below 1 year (< 1 yr), between 1 and 2 years (1-2 yr), and more than 2 years (> 2 yr). The occurrence of sleep-related respiratory disorders decreased with the increase of disease duration (23 +/- 15; 18 +/- 14; and 16 +/- 15 events per hour respectively), the decrease being significantly lower in the > 2 yr group than in the < 1 yr (p < 0.05). Again ODI was similar in the three groups. In conclusion the present study shows that sleep-related breathing events are more common than previously described in ALS patients, particularly in the first year following onset of the disease. Obstructive events occur rarely, although the prevalence of obstructive sleep apnea is higher than predicted, particularly when bulbar symptoms are present. Patients without bulbar signs show a higher prevalence of central events. The progressive decrease of events with the increase of disease duration could be due to a progressive weakness of respiratory muscles, but it could also suggest an independent role for nocturnal events which could be linked to a worse prognosis or to a more rapid decay of clinical status.