BACKGROUND: Solid organ transplanted patients have a three- to fourfold higher lifetime risk of developing a cancer than the general population. However, the incidence of a second primary cancer in transplanted patients has never been studied, despite the fact that the presence of regular follow-ups and the increased survival of these patients make them a very attractive model. METHODS: We investigated the incidence of a second primary cancer (SPC) in 7,636 patients who underwent a kidney, liver, lung or heart transplant between 1970 and 2004, and were followed-up for 51,819 person-years. RESULTS: During the follow-up, 499 subjects developed a first cancer (annual incidence: 98.6 x 10,000 PY), and 22 of them developed a SPC (annual incidence: 3.9 x 10,000 PY). The annual incidence of a SPC in the transplanted patients who developed a first cancer was 107.8 x 10,000 PY, giving a standardized incidence ratio of 1.1 (95% CI: 0.83-1.41). CONCLUSIONS: This result shows that the incidence of the SPC was the same as the incidence of a first cancer. Our study does not indicate an increased risk of SPC in transplanted subjects who already suffered a first malignancy.