We treated 500 patients with high-dose chemotherapy (HDC) and autologous bone marrow (ABMT) or autologous peripheral blood stem cell transplantation (PBSCT). Treated conditions included leukemia, lymphomas, breast cancer, lung cancer, germ-cell carcinomas, and other solid tumors. In order to assess relapse of primary malignancy or occurrence of new neoplasms, routine screening after ABMT or PBPCT was performed at regular and close intervals. With a total follow-up of 1358 person-years and a median follow-up of 34 months (range 9-91), 10/500 (2%) patients developed second malignancies after PBSCT or ABMT; i.e., one new cancer occurred every 136 person-years. All malignancies were detected at routine follow-up examinations; and 7/10 diagnoses were made in an asymptomatic phase; 6/10 neoplasms were amenable to complete surgical resection, five of which remain in CR at a median of 23+ months after autotransplantation. We conclude that regular and close follow-up examination of patients after autologous hematopoietic stem cell transplantation may be beneficial, since successful treatment of second malignancies is possible in selected cases after early detection.