The temozolomide is a promising orally cytotoxic agent used in malignant glioma. The survival curve improvement after drug administration appears to be statistically significant. The review of temozolomide side effects is carried out by search on literature data found on web and is divided on the 4 grades of toxicity according to the National Cancer Institute Common Toxicity Criteria, version 2.0. The adverse effects related with TMZ administration are divided in three categories: myelosuppression, non haematologic toxicity, and infections. The main adverse effect is the myelosuppression that appears to be rather low and reversible as well as the vomiting or nausea. The different schedules of administration are analysed. The frequency of concomitant infections is underlined. In particular, if available, the relationship between temozolomide and other cytotoxic agents or anticonvulsivant drugs is analysed to clarify the possibility of increase of toxicity. The temozolomide is used also in children but the toxicity could be more frequent.