OBJECTIVE Some studies have indicated an increased incidence of neoplasia, particularly breast and colon, in acromegaly. We have determined the incidence of benign and malignant neoplasms in an Australian population of patients with acromegaly. DESIGN Retrospective review, with comparison against cancer data for the local population obtained from a State Cancer Registry. PATIENTS Fifty patients with documented acromegaly. RESULTS There were 7 cases of malignancy (2 in men, 5 in women) in the period of follow-up (435 patient years). With logistic regression analysis, there was a relative risk of malignancy, of 1.2 (95% confidence interval 0.31-5.0) for men (P = 0.8) and 4.3 (95% confidence interval 1.7-10.5) for women (P = 0.001), when compared to the local population. There were 2 cases of breast and renal carcinoma, and one each of prostatic, colonic and parotid carcinoma. Of the most common benign tumours 35% of patients had thyroid nodules, 10% had colonic polyps and 6% had nasal polyps. CONCLUSION The incidence of malignancy was found to be increased in female patients with acromegaly in this series. Routine screening procedures for malignancy, particularly in female patients, should therefore be considered.