Abstract Patients with schizophrenia who develop cancer often have a variety of complicated medical and psychiatric problems. Problems associated with receiving a diagnosis of cancer and with understanding or cooperating with medical treatment may develop. Research in managing and treating schizophrenia patients with cancer is scarce. Presented herein is the experience of the authors’ consultation–liaison psychiatry service in treating patients with schizophrenia who have cancer, and discussion of the medical management of such cases. Fourteen patients were treated between April 1999 and March 2003 and included patients receiving consultation psychiatric services at Shimane University Hospital as well as patients referred from other psychiatric hospitals. These patients were divided into two groups based on whether they were amenable to cancer treatment or not. The treated group consisted of patients who accepted cancer treatment, and the untreated group consisted of patients who refused or interrupted the cancer treatment. The clinical course, clinical psychiatric symptoms, problems in understanding cancer, cancer treatment course and convalescence were retrospectively assessed. Psychiatric symptoms and state were measured using the Brief Psychiatric Rating Scale (BPRS) and the Positive and Negative Syndrome Scale (PANSS). The mean of the duration of schizophrenia in these two groups was not significantly different. The mean scores on measures of psychiatric symptoms in each group (treated and untreated) were as follows: BPRS, 45.3 ± 15.4 and 64.9 ± 9.2 (P < 0.05); positive symptoms scores on PANSS, 14.4 ± 8.8 and 20.6 ± 6.0 (NS); negative symptoms scores on PANSS, 20.6 ± 4.7 and 33.6 ± 4.4 (P < 0.01); and total scores on PANSS, 31.7 ± 7.0 and 48.6 ± 7.4 (P < 0.01). Patients with severe negative symptoms had greater difficulty understanding and cooperating with the cancer treatment. Regarding cancer stage, when cancer was discovered, the disease had already advanced and was no longer amenable to first-line treatment. Regarding notification of the diagnosis, it was rarely possible to give sufficiently early notice to patients in the untreated group. The important role of consultation–liaison psychiatrist in treating cancer patients is suggested. Some steps are proposed for managing schizophrenia patients with cancer who are not able to give informed consent.