The aim of this study was to analyze sleep complaints in patients with systemic lupus erythematosus (SLE) and to determine its prevalence and associations. Fifty outpatients with SLE and an equal number of age- and sex-matched controls were included in the study. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) in both cases and controls. Depressed mood, functional disability and pain severity were assessed in patients using standardized questionnaires. Disease severity, cumulative damage and presence of fibromyalgia were determined by clinical examination. Bivariate associations between sleep quality and disease-related variables as well as demographic variables were calculated. A series of hierarchical regression analyses were computed to determine the independent determinant of sleep quality. PSQI scores were significantly higher in patients with SLE. Prevalence of sleep disturbance was 62%. Functional disability, disease activity and depressed mood correlated positively with sleep disturbances. 36% of the patients satisfied ACR criteria for fibromyalgia. In multiple regression analyses disease activity was found to be an independent determinant of sleep quality. The prevalence of poor sleep quality in patients with SLE was higher than it is generally perceived to be. Functional disability, disease activity and depressed mood contributed significantly to sleep disturbances in SLE.