We conducted this study to clarify the current trends and healthcare resource usage in the treatment of inpatients with primary malignant brain tumors. The Diagnostic Procedure Combination (DPC) data of all inpatients treated between 2013 and 2014 in the 370 core and branch hospitals enrolled in the Japanese Neurosurgical Society training program were collected. DPC is a discharge abstract and administrative claims database of inpatients. We assessed 6,142 primary, malignant brain tumor patients. Patient information, diagnostic information, treatment procedure, and healthcare resource usage were analyzed. Chemotherapy was the most frequent treatment (27% of cases), followed by surgery (13%) and surgery + chemo-radiotherapy (11%). Temozolomide (TMZ), the most frequently used chemotherapeutic drug, was administered to 1,236 patients. Concomitant TMZ and radiotherapy was administered to 816 patients, and was performed according to the Stupp regimen in many cases. The mean length of hospital stay (LOS) was 16 days, and the mean medical cost was 1,077,690 yen. The average medical cost of TMZ-only treatment was 1,138,620 yen whilst it was 4,424,300 yen in concomitant TMZ patients. The LOS was significantly shorter in high-volume than in low-volume hospitals, and the medical cost was higher in hospitals treating 21-50 patients compared to those treating 1-10 patients. However, the direct medical cost of TMZ treatment was the same across different volume hospitals. This is the first report of current trends and healthcare resource usage in the treatment of primary malignant brain tumor inpatients in the TMZ era in Japan.