This study focused on the relative utility of the model of human occupation for occupational therapy assessment of persons having mental disorders. The organizational status of the human system and its relationship to adaptive level of functioning and degree of symptomatology were examined in a sample of 30 adult psychiatric patients. We used a six-test assessment battery developed for this study, which was based on the model of human occupation, to measure the organizational status of the following components of the human system: locus of control, goals, temporal orientation, interests, roles, and skills. Subtests of the American Association on Mental Deficiency (AAMD) Adoptive Behavior Scale and the Modified Brief Psychiatric Rating Scale were used to measure adaptive level functioning and symptomatology, respectively. When we compared organizational status with psychiatric diagnosis and symptomatology, we found organizational status to be the more significant index of adaptive level of functioning.