Purpose/aim of the study: Our objective was to determine the risk of a subsequent malignancy in patients with glioblastoma multiforme (GBM). Materials and methods: Data of patients with a primary diagnosis of GBM were extracted from the Surveillance, Epidemiology, and End Results database. Patients were divided into three age groups: pediatric, <= 19 years of age; adult, 20-59 years; elderly, >= 60 years. Outcomes were overall survival and incidence of second cancer. Results: A total of 24 348 patients with primary GBM were identified during the period from 2004 to 2013: 349 pediatric, 9841 adults and 14 518 elderly. There were significant differences in terms of sex, race, registry site, tumor histological type, tumor size and extension among the groups. The median survival time for pediatric, adult and elderly patients was 15, 15 and 5 months, respectively. Of the study population, 1.8% developed a second malignancy and the rates of the three groups were statistically different. Secondary tumors of the cranial nerves and other nervous system were the most common occurrence in the adults and elderly. Female, registry site, giant cell glioblastoma, undergoing surgery or radiation therapy were associated with developing a second malignancy. Conclusions: The risk of a second malignancy in GBM patients is 1.8%, and associated with certain patient and treatment factors.