Various polysomnographic sleep patterns are associated with affective disorders, but very little is known about sleep spindle characteristics in adult depression. In primary endogenous depressive male patients (unipolar, UP, and bipolar, BP) with comparable depression scores and in normal control subjects recorded during 3 consecutive nights, no night effect was observed on the sleep variables investigated except for REM latencies of stages 1 and 2. Stage 2 duration and variables related to sleep spindle characteristics (the number and the density of spindles of 1/2 s; the number and the density of full spindles of stage 2 over the 3 nights) were significantly lower in depressed patients than in control subjects, the mean number of spindles being lower in UP than in BP patients. Sleep spindle measures were clearly negatively correlated with age in the overall group (i.e., depressed plus control subjects). They were also negatively correlated with the REM latencies of stages 1 and 2 in BP depressed patients, whereas this relation was not observed in UP patients.