Sleep disorders have been reported as a frequent problem in dialysis patients. However, only one paper has compared the prevalence and possible causes of this complication in peritoneal (PD) and haemodialysis (HD) patients. We surveyed 84 PD and 87 HD patients about disordered sleep using a self-administered questionnaire. Forty-nine percent of PD and 56% of HD patients reported problems sleeping. These problems were rated as severe by 29 PD and 22 HD patients. Type of disturbances involved delayed sleeping (13 PD and 32 HD, p < 0.005), interrupted sleep (32 PD and 44 HD) and early morning awakening (25 PD and 37 HD). The number of hours of sleep varied widely among patients: it was 5 and 21 minutes in PD patients with sleep disorders and 7 and 37 min in PD pts without such problems. No statistically significant relationship was evidenced between sleep disorders and age, sex, body weight, obesity, duration of dialysis, dialysis dose, self-assessed sadness, anxiety, worry, pain, pruritus, dyspnoea, restless leg syndrome, use of cigarettes, caffeine, or sleeping pills. In conclusion, sleep disorders are a frequent problem in both PD and HD patients. Apparently the relationship with demographics, dialysis dose, lifestyle and personality traits is poor. The possible role of other causes should be investigated.