Megestrol acetate is a semi-synthetic progestational steroid that was originally used as a therapeutic modality for metastatic breast and endometrial cancers. What was originally considered to be it's most frequent side effect, an increase in appetite and in body weight, has gradually become an established treatment of malnutrition in patients with the acquired immuno-deficiency syndrome or with non-hormone responsive cancers. The use of megestrol acetate in treating malnutrition in older persons, in patients on dialysis and in a number of other situations is currently under investigation. The authors review the evidence available to support the use of megestrol acetate in treating malnutrition in these selected groups, and the problems associated with administering megestrol acetate; they also report on their own experience with megestrol acetate in the geriatric population.