To evaluate the incidence, risk factors and prognosis for solid tumors after hematopoietic stem cell transplantation (HSCT) in Japan, 809 patients who had received HSCT between 1981 and 2000 were retrospectively analyzed. In all, 19 newly diagnosed secondary cancers were observed. The risk for cancer development was 2.8 times as high as that for expected cases. The cumulative incidence ratios at 5 and 10 years were 1.9 and 4.2%, respectively. The risk was significantly elevated for buccal cavity cancer (standard incidental ratio (SIR), 44.42: 95% confidence interval (CI) 17.86-91.51), esophageal cancer (SIR, 22.36: 95% CI 6.09-57.25), and cervical cancer (SIR, 8.58: 95% CI 1.04-31.01). Of 15 patients who developed solid cancers following allografting, 12 had chronic graft-versus-host disease (GVHD), and all 10 patients with squamous cell carcinoma of the buccal cavity or esophagus had chronic GVHD. On multivariate analysis, extensive chronic GVHD and age over 45 years at the time of transplantation were associated with a higher risk for solid cancers. In all, 17 patients received therapy for secondary cancers, nine of whom are still alive and the 5-year probability of survival from the diagnosis is 42.8%. Our data suggest that early detection of secondary cancers is very important in prolonging overall survival.