OBJECTIVE: We examined the efficacy of a case management approach to improve participation in colorectal cancer screening among people with schizophrenia. METHODS: This was a randomized, parallel group trial. We recruited outpatients with schizophrenia aged 40 years or over from two psychiatric hospitals in Japan. Participants were randomly assigned (1:1) to treatment as usual or case management intervention plus treatment as usual using a web-based system. Attending clinicians and participants were unmasked to the allocation. Case management included education and patient navigation for colorectal cancer screening using a fecal occult blood test. Treatment as usual included direct mail government recommendations. The primary endpoint was participation in colorectal cancer screening assessed using municipal records. We also assessed the secondary endpoint of participation in other cancer screenings (lung, gastric, breast, and cervical). RESULTS: Between 3 June and 9 September 2019, 172 eligible participants were randomly assigned to the case management plus treatment as usual group (n = 86) or treatment as usual group (n = 86). One participant was ineligible and another withdrew consent; both were excluded from analysis. A significantly higher proportion of participants received colorectal cancer screening in the case management plus treatment as usual group than in the treatment as usual group (40 [47.1%] of 85 participants vs. 10 [11.8%] of 85 participants, p < 0.0001). The proportion of lung cancer screening also increased. No serious adverse events associated with the study intervention occurred. CONCLUSION: The case management intervention to encourage participation in colorectal cancer screening was effective for patients with schizophrenia.