Acromegaly patients are known to have an increased risk of malignancies, especially colonic adenocarcinoma. This may be as a result of the growth-stimulating effect of growth hormone (GH). The clustering of leukaemia in children treated with GH has also caused concern. There have been a few reports of leukaemia in acromegaly patients. We report two patients with acute lymphoblastic leukaemia and one patient with acute myeloid leukaemia among 106 acromegaly patients treated over a 15-year period. Two of the cases received radiotherapy as part of their treatment. Adjusted for age and follow-up years, the incidence of leukaemia in this cohort is significantly higher than the general population. The incidence is also higher than would be expected as a result of radiotherapy alone, suggesting that GH may play a synergistic role.