Leptin, involved in energy regulation and contributor to cardiovascular disease, has been implicated to play a role in depression and sleep disturbances, two closely intertwined conditions. Previous results investigating leptin level alterations either in sleep disorders or in depression have been inconsistent. We investigate the association between leptin levels and the different combinations of depressed mood and sleep disturbances in 1369 subjects (706 men, 663 women), derived from the population-based MONIKA/KORA study. As leptin regulation is known to differ by sex and weight, analyses were performed in normal weight and overweight men and women separately. We found a highly significant association between leptin levels and the combination of depressed mood and sleep disturbances in normal-weight women (BMI