Pathologic nocturnal eating can be associated with a heterogeneous group of medical and psychiatric disorders. The current study was designed to evaluate the prevalence and clinical features of nocturnal eating syndrome (NES), a major subtype of pathological nocturnal eating. Conducted prospectively over an 18-month period (January 1994-June 1995), the study consisted of clinical, psychological, and polysomnographic assessments of 120 adult subjects (51 males, 69 females; mean age 42.6 years, range 18-86 years) who were either self-referrals (58%) or physician referrals (42%) to our Sleep Disorders Center for insomnia complaints. Nocturnal eating with features that are typical of NES, namely compulsive feeding shortly after a mid-non-rapid eye movement (NREM) sleep awakening, in the absence of daytime eating disorders, occurred in seven subjects (five females, two males; mean age 50.8 +/- 9.5 years; mean age at onset of NES 42 years, range 18-61 years), or 5.8% of the sample. NES accounted for 44.4% of all the nocturnal eating cases observed. The data suggest that an adult, late-onset variety of NES is not infrequent. Several of the clinical features of our NES patient series correspond closely to most of those observed in other descriptions of NES in the literature. Overall, the data reinforce the idea that NES is a distinct syndrome, even though some of its features overlap with sleep-related eating disorders (e.g. associated with sleepwalking, restless legs syndrome, obstructive sleep apnea, etc.) and with eating disorders such as daytime binge eating.