The prevalence of known cases of acromegaly in Northern Ireland in 1984 was 6.3 per 100,000 population. The incidence of newly-diagnosed cases over the preceding 25 years was 5.5 patients per year, or 0.4 patients per 100,000 population per year. This rate would be equivalent to about 200 new cases per year in the United Kingdom. Four options have been available to most of these patients--surgical hypophysectomy (transfrontal or transsphenoidal), pituitary radiotherapy (usually external cobalt beam), drug treatment with bromocriptine, or no treatment. Choice of treatment has been mainly influenced by tumour size, with the larger pituitary adenomas having surgery initially. No single form of treatment has been successful in achieving a clinical remission or cure in more than a minority of cases. The most successful outcome has been where total pituitary ablation has been achieved. Life-table analysis for the whole group shows life expectancy which is not markedly different for that of an age-matched population from Northern Ireland. Morbidity related to long term osteoarthritis and treatment complications remain a major problem. The incidence of malignant tumours is higher than would be expected.