Twenty-four drug-free patients with a DSM-III diagnosis of panic disorders (and their age- and sex-matched normal controls) slept in the laboratory for 3 consecutive nights. Panic patients showed a slightly longer sleep latency and a lower sleep efficiency than their normal controls. They also had more overall movement time and more body movements during stage 2 sleep. Eight panic attacks were recorded arising out of sleep. Six of them occurred in the transition phase between stage 2 and stage 3 sleep. The nocturnal panic attacks of these patients are unique, different from stage 4 sleep terrors, and different from dream anxiety attacks.