Endocrine complications of human immunodeficiency virus (HIV) and its treatment are being increasingly recognized. We discuss the diagnosis and management of an HIV seropositive man who presented with bilateral gynaecomastia and 'hyperprolactinaemia' due to macroprolactin within six months of starting antiretroviral therapy. We suggest that the gynaecomastia may be a feature of immune reconstitution disease. Measurement of serum prolactin in the investigation of gynaecomastia should be reserved for those with hypogonadotrophic hypogonadism. Since macroprolactin contributes to circulating prolactin in HIV-seropositive subjects, hyperprolactinaemic samples in these patients should be tested for macroprolactin.