BACKGROUND/AIM:This study was conducted retrospectively to evaluate rates of thrombocytopenia and their clinical impact during chemo-radiotherapy for glioblastomas and to elucidate associated clinical factors. METHODS:A total of 64 patients who received temozolomide chemotherapy at our institution was included; 35 patients received full-dose chemo-radiotherapy as per the STUPP protocol (Group A), and 9 patients received abbreviated radiotherapy with concurrent chemotherapy (Group B). Twenty patients received temozolomide alone with an intended 12 cycles of therapy for first relapse at least 6 months after completion of adjuvant chemotherapy (Group C). RESULTS:In Group A, 27 of 35 (77%) patients completed the chemo-radiotherapy phase; 14% had grade 3-4 thrombocytopenia leading to discontinuation. Of 27 patients, 16 (59%) completed adjuvant chemotherapy. There were no grade 3-4 thrombocytopenias, but 4% discontinued due to grade 2 thrombocytopenias. In Group B, four of nine (45%) patients completed the chemo-radiotherapy phase; 11% had grade 3-4 thrombocytopenias and discontinued treatment. Three of four (75%) patients completed adjuvant chemotherapy. Of these, 75% had grade 3-4 thrombocytopenias, but none discontinued. Finally, in Group C, 8 of 20 (40%) patients completed, with 10% discontinuing due to thrombocytopenias and the rest due to disease progression. In exploratory analyses, being female increased the risk of myelosuppresion, and there was a trend noticed in patients having a higher body surface area. CONCLUSION:Our toxicity data were within range of the literature. We identified the group of patients that have increased thrombocytopenia risk. Larger pooled retrospective series and prospective studies are required.