This study assessed the risk of skin cancer following transplantation of 4 types of solid organs, and the risk of skin cancer in patients with chronic diseases that lead to organ transplantations. A population-based cohort of 5279 Danish patients who underwent heart, lung, renal and liver transplantation, and 77,782 patients with chronic heart, lung, renal and liver diseases during 1977-2006 were included in the study. Linkage to the Danish Cancer Registry allowed complete follow-up for basal cell carcinoma, squamous cell carcinoma and malignant melanoma. Standardized incidence ratios (SIR) and 95% confidence intervals (CI) were calculated. The SIR for squamous cell carcinoma was highest among heart (SIR = 113; 95% CI: 74-166), then renal (SIR = 81; 95% CI: 68-96), lung (SIR = 65; 95% CI: 28-128) and liver (SIR = 60; 95% CI: 27-113) recipients. SIR for squamous cell carcinoma was 4.8 (95% CI: 2.2-9.0) among renal failure patients, but not greatly elevated among patients with the other chronic diseases studied. Organ transplantation is a risk factor for squamous cell carcinoma, with immunosuppressive treatments being the most likely explanation for the association.