Background: Medulloblastomas are malignancies of the posterior fossa with metastatic potential to the central nervous system. While a common pediatric malignancy, they are rare in adults. Extrapolating treatment regimens from pediatrics to adults is fraught as adults can developmentally tolerate higher radiation doses, but have less bone marrow reserve and therefore risk higher myelosuppressive toxicities with adjuvant systemic therapy. A standard systemic regimen for adults has not been delineated, though craniospinal radiation alone is likely insufficient in most cases. In the absence of well-established guidelines, our institution has historically used a combination of cisplatin (60 mg/m2 on Day 1) and etoposide (60-120 mg/m2 on Days 1-3 or 1-5) repeated in three-week cycles for three to a maximum of six cycles, but the literature to support this regimen is scant. Methods: In this retrospective chart evaluation, we reviewed the medical information of patients who were seen for newly diagnosed adult medulloblastoma between 1995 and 2020 at Johns Hopkins Hospitals. Those who met our pre-specified criteria (adjuvant treatment with etoposide/cisplatin within six months of craniospinal irradiation, sufficient data on toxicity before and after radiation, during chemotherapy, and one month after completion of the regimen, as well as sufficient clinical follow-up) were included in the analysis. Hematological toxicities were graded by NCI CTCAE guidelines. Follow-up for progression and survival were calculated from the end of the last chemotherapy administration and plotted on swimmers plots. Results: Ten out of 74 total adult medulloblastoma patients had adequate data about the tolerability of the regimen and clinical follow-up. Median time to follow-up was 46 months (range 4.5-164 months). Eight patients experienced Grade 3 and 4 hematological toxicities. Seven patients completed their planned treatment course, while two patients discontinued treatment prematurely because of hematological toxicities and one due to ototoxicity and fatigue. Three out of the ten patients progressed post-chemotherapy at 1 month, 24.5 months, and 44 months. Both early-progression patients died (7 and 29.5 months respectively), while the remaining eight are alive without evidence of progression. Conclusions: The data suggest a combination regimen of cisplatin and etoposide after craniospinal radiation in newly diagnosed adult medulloblastoma patients has acceptable toxicity and survival outcomes in this small patient cohort and compare favorably to other limited datasets in the literature. Further study is warranted to validate this as a recommended regimen.