Perceived control is of significance in occupational therapy, as revealed in empirical research and suggested in practice models. This study investigated the relationship between perceived control and occupational performance in persons with long-term mental illness. The 177 participants were assessed regarding perceived control (locus of control and self-mastery) and occupational performance (activity level and satisfaction with daily occupations). Subgroups with respect to diagnosis and having gainful employment or not were also explored concerning the targeted association. The results indicated relationships between perceived control and occupational performance in the sample as a whole and in all subgroups except that representing people engaged in gainful employment or education. The latter was a surprising result, considering that the importance of perceived control was originally identified in the work science area. The results strongly supported that perceived control should be included in the clinical reasoning of occupational therapists working in mental health care.