Posttransplant malignancies have become a serious long-term complication after liver transplantation. Our aim was to compare the incidence of posttransplant cancers with national cancer incidence rates. The study included all Finnish liver transplant patients transplanted at the Helsinki University Central Hospital between 1982 and 2005. The cohort was linked with the nationwide Finnish Cancer Registry. Observed numbers of cancers were compared to site-specific expected numbers based on national cancer incidence rates stratified by age, sex, and calendar time. The standardized incidence ratios (SIRs) were calculated as observed-to-expected ratios. Thirty-nine posttransplant de novo cancers and 11 basal cell carcinomas were found in the cohort of 540 patients during 3222 person years of follow-up. The overall SIR was 2.59 (95% confidence interval 1.84-3.53). SIR was higher for males (SIR 4.16) than for females (SIR 1.74), higher among children (SIR 18.1) than among adults (SIR 5.77 for ages of 17-39 years and 2.27 for ages >/= 40 years), and more elevated in the immediate posttransplant period (SIR 3.71 at 10 years). The most common cancer types were nonmelanoma skin cancer (SIR 38.5) and non-Hodgkin lymphoma (SIR 13.9). Non-Hodgkin lymphoma was associated with male gender, young age, and the immediate posttransplant period, whereas old age and antibody induction therapy increased skin cancer risk. In conclusion, cancer incidence is increased among liver transplant patients compared to the general population. This study points out the importance of cancer surveillance after liver transplantation.