Adult malignant brainstem gliomas (BSGs) are poorly characterized due to their relative rarity. We have examined histopathologically confirmed cases of adult malignant BSGs to better characterize the patient and tumor features and outcomes, including the natural history, presentation, imaging, molecular characteristics, prognostic factors, and appropriate treatments. A total of 34 patients were identified, consisting of 22 anaplastic astrocytomas (AAs) and 12 glioblastomas (GBMs). The overall median survival for all patients was 25.8 months, with patients having GBMs experiencing significantly worse survival (12.1 vs. 77.0 months, p = 0.0011). The majority of tumors revealed immunoreactivity for EGFR (93.3 %) and MGMT (64.7 %). Most tumors also exhibited chromosomal abnormalities affecting the loci of epidermal growth factor receptor (92.9 %), MET (100 %), PTEN (61.5 %), and 9p21 (80 %). AAs more commonly appeared diffusely enhancing (50.0 vs. 27.3 %) or diffusely nonenhancing (25.0 vs. 0.0 %), while GBMs were more likely to exhibit focal enhancement (54.6 vs. 10.0 %). Multivariate analysis revealed confirmed histopathology for GBM to significantly affect survival (HR 4.80; 95 % CI 1.86-12.4; p = 0.0012). In conclusion, adult malignant BSGs have an overall poor prognosis, with GBM tumors faring significantly worse than AAs. As AAs and GBMs have differing imaging characteristics, tissue diagnosis may be necessary to accurately determine patient prognosis and identify molecular characteristics which may aid in the treatment of these aggressive tumors.