Background: A recent United Kingdom (UK) report found that breast and colorectal cancers were more common in people with severe mental illness (SMI) and recommended targeted screening. Epidemiological evidence is however inconsistent. Objectives: To estimate relative incidence rates for colorectal, breast and lung cancer, and the overall incidence of the commonest other UK cancers, in people with SMI compared with people without SMI. Method: Cohort study in the UK using The Health Improvement Network (THIN) primary care database between 1990 and June 2008. Poisson regression was used to obtain adjusted incidence rate ratios (IRRs) for cancer, comparing two cohorts of people over 18; with and without a diagnosis of SMI. Results: We identified 20,632 people with SMI and 116,152 people without, with median follow up of over 6. years. No significant associations were observed between SMI and cancers of the breast (adjusted IRR 1.17; 95% confidence interval 0.95-1.45), colon (0.70; 0.46-1.05), rectum (1.05; 0.65-1.69) or lung (0.84; 0.65-1.10). The adjusted IRR for an aggregate cancer outcome in SMI was 0.95; 0.85-1.06. Results were similar for schizophrenia and bipolar disorder. Conclusions: In a cohort analysis within a large UK primary care database, the incidence of colo-rectal, breast and lung cancer, and of all common cancers, did not differ significantly in people with SMI, including schizophrenia, compared with people without SMI. Our results do not support enhanced screening procedures for cancer in people with SMI. © 2012 Elsevier B.V.