Objective: This study tested the effectiveness of a nurse-delivered health check with the Health Improvement Profile (HIP), which takes approximately 1.5 hours to complete and code, for persons with severe mental illness. Methods: A single-blind, cluster-randomized controlled trial was conducted in England to test whether health checks improved the general medical well-being of persons with severe mental illness at 12-month follow-up. Results: Sixty nurses were randomly assigned to the HIP group or the treatment-as-usual group. From their case lists, 173 patients agreed to participate. HIP group nurses completed health checks for 38 of their 90 patients (42%) at baseline and 22 (24%) at follow-up. No significant between-group differences were noted in patients’ general medical well-being at follow-up. Conclusions: Nurses who had volunteered for a clinical trial administered health checks only to a minority of participating patients, suggesting that it may not be feasible to undertake such lengthy structured health checks in routine practice.