The authors conducted a preliminary examination of treatment-related decision-making capacity (DMC) in middle-aged and older psychosis patients. The MacArthur Competency Assessment Tool for Treatment (MacCAT-T) was administered to measure DMC among 16 patients with psychotic disorders and without dementia (mean age: 54.6 [SD 7.2] years). The impact of repeated learning trials on patients' understanding was assessed with the Hopkins Competency Assessment Test (HCAT). Subjects were also assessed with the Positive And Negative Syndrome Scale and Mattis' Dementia Rating Scale. There was a wide range of performance on the MacCAT-T; the levels and range of MacCAT-T scores were similar to those previously reported among younger acutely hospitalized patients in the MacCAT-T validation study. Patients' understanding of disclosed material on the HCAT improved significantly over repeated presentations. Although there were no statistically significant correlations observed between DMC and demographic characteristics, severity of symptoms, or global cognitive deficits, the sample size provided limited power to detect such associations. Results point to the importance of assessing DMC and to the potential modifiability of initial difficulties in understanding.