This study was aimed at investigating the outcomes of an activity-based assessment (BIA) compared with standard assessment (SA) for evaluating clients undergoing psychiatric occupational therapy. Patients admitted to a psychiatric occupational therapy unit were randomized into the BIA or the SA assessment. The outcome indicators were (a) clients’ satisfaction with the occupational therapy during the assessment period, (b) clients’ awareness of capacities and occupational problems, (c) satisfaction with the assessment among the referring physicians, and (d) outcomes of the intervention following the assessment, in terms of changes in occupational performance and satisfaction. The groups did not differ in awareness of occupational problems, but the BIA group was more satisfied than the SA group with the support of their contact person and with the group leader during the period of assessment. Furthermore, physicians receiving feedback on patients in the BIA group were more satisfied than those receiving feedback on patients in the SA group. However, the groups did not differ concerning change during the treatment period in occupational performance or satisfaction. Thus, there was no difference between the assessment methods regarding the outcomes of the treatment following assessment. Minor advantages from the patients’ perspective were found, in terms of better satisfaction in the BIA group, and from the referring physicians’ perspective the BIA clearly seemed more satisfying than the SA. Thus, the findings showed that the BIA possessed better qualities than the SA regarding the indicators pertaining to satisfaction, but not concerning awareness of capacities and problems or the outcome of the subsequent treatment.