Cotherapy has been advocated as an effective treatment mode, especially with groups, couples, and families. The relationship between the cotherapists has been identified as an important determinant in the success of this method. This relationship has been compared to the marital relationship between spouses, and the marriages of therapists have been viewed as offering advantages for cotherapy. Since not all therapists who are married to each other work as cotherapists, the purpose of this study was to investigate whether or not spouse cotherapists differ from other therapists who are also married to each other but who do not work together on a regular basis as cotherapists. The five dimensions measured for all subject couples include frequency of differing theoretical orientation, similarity of self-reported behavior in therapy, compatibility of needs for inclusion, compatibility of needs for control, and compatibility of needs for affection. Subjects for this study were 6 5 married couples in which both spouses were psychotherapists. The couples were divided into two groups according to whether or not they worked together as cotherapists on a regular basis. The group of spouse cotherapists included 29 couples who reported regular cotherapy together. The group of therapist couples included 37 couples who reported no regular cotherapy with their spouses. All subject couples were provided a packet of materials which included a letter explaining the general purpose of the study, two copies of the Therapist Personal Data Form, two copies of the Self-Description of Therapist's Behavior, two copies of the Fundamental Interpersonal Relations Orientation-Behavior, and a stamped envelope addressed to the experimenter for the return of the materials.