Abstract This study examined the sleep and mood differences between premenopausal and perimenopausal women matched for age and sociodemographic variables. Wrist actigraphy, Profile of Mood State (POMS), State-Trait Anxiety Inventory (STAI), a sleep questionnaire, and responses to a sleep diary were recorded for a period of 1 week. It was found that the sleep disruption of perimenopausal subjects was significantly greater than that of the premenopausal group ( p<0.05). Overall, the perimenopausal group demonstrated a significant increase in sleep disruption and mood alterations when compared with the premenopausal group. Actigraphic data showed that perimenopausal subjects experienced longer and more numerous arousals resulting in significantly less sleep ( p<0.05). In addition, perimenopausal subjects scored significantly higher ( p<0.05) on the STAI and significantly lower on the Vigor subscale of the POMS ( p<0.01) than premenopausal subjects. Correlational analyses indicated that sleep and mood changes were significantly related in the perimenopausal group, but not in the premenopausal group. Taken together, these results suggest that the mood changes experienced by the perimenopausal group may be mediated by sleep disruption.