A review of the current literature on cotherapy with special reference to therapeutic outcome is presented. The review covers the fields of sex therapy, group therapy, and family and marital therapy. It considers both patient variables and cotherapist variables. There are few "research" studies of cotherapy. Most data derive from case illustrations which, however well detailed, are anecdotal in nature. The most widely addressed effect of cotherapy upon patients is presented in terms of treatment process and not treatment outcome.