Seasonal distribution of birth rates was only recently described in patients with high-grade gliomas. We analyzed 501 cases from the database of a Regional Cancer Center in Bavaria to assess annual periodicity in the birth dates of glioma patients. Prior to analysis, the number of births per month was normalized [number of births x 100,000/total number of births in Germany] to obtain birth rates per month. The approximation of the time series data by a one-year cosine model found that the glioblastoma birth rate exhibits a statistically significant annual variation, with the peak rate in January. Vitamin intake, infections, and other as-yet-unknown factors and exposures during pre- and perinatal early life may contribute to the seasonality of birth rate in patients with brain tumors.