Temozolomide has been available to oncologists for over 30 years. During this time, it has become an integral part of standard therapy in patients with high-grade gliomas. Given its ability to traverse the blood-brain barrier, temozolomide has also been evaluated in other cancers that involve the central nervous system (CNS). We review its role in the management of patients with primary brain tumors, brain metastases, leptomeningeal carcinomatosis, and other selected CNS cancers. There is strong evidence that temozolomide is effective in patients with high-grade astrocytomas and oligodendrogliomas. Modest evidence supports its activity in primary CNS lymphomas and aggressive pituitary adenomas. Temozolomide, however, has minimal efficacy in a wide variety of systemic cancers. Given that concentrations of temozolomide in the CNS are only 20% of those in the blood, it is not surprising that it is generally inactive in patients with CNS metastases from solid tumors.