All night EEG sleep recordings and clinical assessments of sleep quality were performed in normal controls, patients with generalized anxiety disorder and primary dysthymia. Patients were selected according to DSM-III R. Changes of sleep architecture, namely a reduction of slow wave sleep, are similar in generalized anxiety and dysthymia. Also the two groups do not exhibit the REM sleep disturbances usually observed in affective illness. Duration and continuity measures are unchanged in dysthymics, but anxious patients show some features of insomnia. The analysis of subjective aspects of sleep showed no relevant differences between the two groups of patients. Using a conventional set of EEG sleep parameters, primary dysthymia seems closer to anxiety disorders than to affective illness. However, the reduction of slow wave sleep in dysthymics and anxious patients may have different pathogenic meanings and the analysis of nonconventional sleep parameters may prove useful in this regard.