Menstrual synchrony was not found for 30 cohabitating lesbian couples (mean time living together, 35 months), for whom 3 months of menstrual data were collected prospectively. A combined analysis with two previous studies of lesbian couples also failed to reveal synchrony. These data are considered together with a previous study of Bedouin couples which found only a moderate degree of synchrony. When women live together for an extensive period of time and have intensive social contact among them, the intensive contact may not be conducive to menstrual synchrony.