Studies show that people with severe mental illness (SMI) have a greater risk of dying from colorectal cancer (CRC). These studies mostly predate the introduction of national bowel cancer screening programmes (NBCSPs) and it is unknown if these have reduced disparity in CRC-related mortality for people with SMI.

We compared mortality rates following CRC diagnosis at colonoscopy between a nationally representative sample of people with and without SMI who participated in Australia’s NBCSP. Participation was defined as the return of a valid immunochemical faecal occult blood test (iFOBT). We also compared mortality rates between people with SMI who did and did not participate in the NBCSP. SMI was defined as receiving two or more Pharmaceutical Benefits Scheme prescriptions for second-generation antipsychotics or lithium.

Amongst NBCSP participants, the incidence of CRC in the SMI cohort was lower than in the controls (hazard ratio [HR] 0.77, 95% confidence interval [CI] 0.61–0.98). In spite of this, their all-cause mortality rate was 1.84 times higher (95% CI 1.12–3.03), although there was only weak evidence of a difference in CRC-specific mortality (HR 1.82; 95% CI 0.93–3.57). People with SMI who participated in the NBCSP had better all-cause survival than those who were invited to participate but did not return a valid iFOBT (HR 0.67, 95% CI 0.50–0.88). The benefit of participation was strongest for males with SMI and included improved all-cause and CRC-specific survival.

Participation in the NBCSP may be associated with improved survival following a CRC diagnosis for people with SMI, especially males, although they still experienced greater mortality than the general population. Approaches to improving CRC outcomes in people with SMI should include targeted screening, and increased awareness about the benefits or participation.

Australian and New Zealand Clinical Trials Registry (Trial ID: ACTRN12620000781943).