Many epidemiologic studies have reported that obesity is associated with short sleep duration. How the degree of obesity or other clinical characteristics of the obese individuals, such as sleep disturbances or emotional stress, define this relation is not known.We studied a random sample of 1300 middle-aged men and women from the Penn State Cohort in the sleep laboratory for one night. Sleep disturbances were recorded as insomnia, excessive daytime sleepiness (EDS) or sleep difficulty. Chronic emotional stress was determined by the Minnesota Multiphasic Personality Inventory-2 (MMPI-2).Obese individuals (body mass index, BMI>30) reported shorter duration of sleep, had a higher incidence of subjective sleep disturbances (47.4 vs 25.5%; P<0.01) and scored higher for chronic emotional stress than nonobese subjects. However, there was no difference in self-reported sleep duration between obese and nonobese individuals without subjective sleep disturbances, while both obese men and women with sleep complaints scored higher in the MMPI-2 compared to obese individuals without sleep complaints. The shortest sleep duration was reported by the obese insomniac patients (5.9 h), followed by obese with EDS (6.3 h) or sleep difficulty (6.6 h). The effect of chronic emotional stress was stronger than that of the BMI on the reported sleep duration, with a synergistic joint effect. The presence of a sleep disturbance was associated with a reduction of reported sleep by 18 min for men and 42 min in women, whereas a 10 kg m(-2) increase of BMI was associated with a 16 and 6 min decrease of sleep in men and women, respectively. Interestingly, there was no association between objective sleep duration and BMI.Self-reported short sleep duration in obese individuals may be a surrogate marker of emotional stress and subjective sleep disturbances, whose detection and management should be the focus of our preventive and therapeutic strategies for obesity.