Individuals with Down syndrome are at decreased risk of developing most types of solid tumors, including central nervous system malignancies. Several mechanisms have been proposed to explain how additional genetic material on chromosome 21 may confer this increased protection. Only two individuals with Down syndrome and meningioma have been described in the medical literature, whose tumors were both World Health Organization (WHO) grade 1. Here, we report the first individual with Down syndrome to our knowledge who developed an atypical meningioma, WHO grade 2. We also provide a hypothesis for how this tumor could have arisen in the setting of trisomy 21.