National statistics in the United States and Canada indicate that following marital separation, the majority of parents settle for sole custody, with the mother as custodian. Also, in the approximately 15% of separations in which custody is disputed, a majority of mothers are awarded sole custody. A review of different views of the reasons for protracted custody disputes shows few authors systematically using data to support their views. A systematic comparison of custodial and noncustodial parents of both sexes showed no difference in their psychiatric histories, marital status and alleged reasons for marital separation. However, clinical recommendations referred more often to unusual circumstances when it was proposed that sole custody go to fathers rather than to mothers.