Temozolomide (TMZ) is an oral chemotherapy first used for pituitary tumours in 2006. Over the past 12 years experience and confidence using this treatment has increased. Temozolomide is effective: with about 50% of cases showing a tumour response. This figure rises to 70% if stable disease is regarded as a tumour response. The effectiveness appears to be similar in both aggressive adenoma and carcinoma. Functioning tumours show a better response as compared with non-functioning. Recent publications demonstrate temozolomide improves overall survival and the use of TMZ has been incorporated into guidelines on aggressive tumour management. TMZ is an oral treatment normally given as a monotherapy for cycles of 5 days every 28 days (200 mg/m2). It is safe and well tolerated. The common side effects are nausea, vomiting and fatigue. Myelosuppression (thrombocytopaenia / neutropenia) occurs in 717% of cases. The decision to initiate temozolomide should be made by a pituitary MDT who have, or can access, the appropriate knowledge and experience. Often TMZ is used for about 12 months but the optimal duration of treatment is an area of uncertainty and relates to the specific circumstances. There is evidence TMZ potentiates radiotherapy. Combination with other agents such as capecitabine has been recommended by some. Most, but not all, series show MGMT depleted tumours (as assessed by immunohistochemistry) have a better clinical response to TMZ as compared with MGMT replete tumours. It is widely accepted that temozolomide should be used to treat pituitary carcinoma and should be used as a salvage treatment in aggressive adenomas refractory to surgery and radiotherapy. Using TMZ earlier in the treatment pathway, such as prior to radiotherapy; or on the basis of anticipated aggressive behaviour is a more controversial area currently being explored.