The purpose of this study was to evaluate the estimated incidence of secondary malignancies post-allogeneic bone marrow transplantation (BMT) in a cohort of adult patients previously reported now with an additional 8.5 years of follow-up. A cohort of 557 patients older than age 16 years underwent allogeneic BMT between June 1970 and November 1993. Histologic reports confirmed the diagnosis of a secondary malignancy. Multivariate Cox proportional hazards method was utilized to investigate predictors for the development of secondary malignancies. In all, 31 patients in this cohort developed a secondary malignancy a median of 6.79 years after their transplant. The estimated cumulative incidence rate of secondary malignancy was 4.2% at 10 years post transplant. When compared to the general population, the estimated observed/expected ratio of new cancer diagnoses was 5.13. On multivariate analysis, older age at the time of transplant was the only significant predictor for development of secondary cancer (P=0.01). The most common malignancies observed were nonmelanomatous skin cancers and squamous cell cancers of the buccal cavity. The risk of developing a secondary malignancy after allogeneic BMT is significant, particularly in older patients. Long-term survivors of transplant require regular monitoring for early signs of cancer, particularly of the skin and oral cavity.