Background: Attenuated androgens control attacks of hereditary angioedema. Short-term studies of such patients treated at our institution with attenuated androgens demonstrated no adverse effects. However, the side-effect frequencies in patients receiving long-term treatment are relatively less well characterized. Objective: To assess the frequencies of various side effects of the attenuated androgen stanozolol in a population of patients with hereditary angioedema treated for 20 to 40 years.Methods: Data on side effects in patients who continued stanozolol therapy since 1987 were obtained by means of questionnaire. Patients were evaluated by physical examination; biochemical assays of hepatic function, serum lipids, and prostate specific antigen; and liver ultrasound.Results: The minimal initial effective dosage of stanozolol was 0.5 to 2.0 mg daily, although most patients achieved symptomatic control and decreased the dose and frequency as the frequency of attacks decreased. Treatment-related symptoms developed in 10 of 21 patients. No interruption in stanozolol therapy was required because symptoms subsided with a reduction in the stanozolol dosage. Adverse side effects included hirsutism, weight gain, menstrual irregularities or postmenopausal bleeding, acne, and mood changes. Liver enzyme assays revealed no persistent abnormalities. Liver ultrasounds in 8 patients revealed 3 abnormalities deemed unrelated to therapy. Five patients had a reduced high-density lipoprotein, and 2 patients had elevated triglycerides.Conclusion: Stanozolol is a safe and effective drug for the long-term management of hereditary angioedema.Clinical Implications: Stanozolol may be used in the long-term treatment of patients with hereditary angioedema provided such patients are closely supervised with routine clinical, biochemical, and radiologic assessments.