It has been hypothesized that the neuropeptide Y (NPY) system is involved in the pathogenesis of mood disorder. In this study, Y(1) and Y(2) receptor mRNA expression levels were analyzed in the dorsolateral prefrontal cortex of subjects affected with major depression, bipolar disorder, or schizophrenia and compared to normal controls. No significant alterations in Y(1) or Y(2) mRNA expression levels were observed between the groups. However, the Y(2) mRNA expression was elevated in layer IV in subjects with suicide as a cause of death. For the Y(1) mRNA expression, there was a negative correlation with increasing subject age in the prefrontal cortex. Analysis of covariance revealed a significant elevation of the Y(1) mRNA expression levels in individuals with a current history of marijuana use but no other drug. In summary, the current results suggest distinct alterations of the prefrontal Y(1) and Y(2) neuronal populations in aging and suicide.