This article explores the duty of health care pro viders to inform patients of the risk of contracting AIDS through blood transfusions that may be neces sitated by surgery or other forms of medical treat ment. Although the quantitative risk of receiving HIV-contaminated blood in a transfusion is small, the qualitative risk is of a magnitude requiring complete disclosure if a patient's consent to treatment is to be considered adequately informed. Recent litigation confirms the importance of providing patients with the information needed to adequately assess the risks and benefits of proposed treatments that might in volve a transfusion and reveals the need to offer the opportunity, where permissible, for autologous and directed donations. A comprehensive program em bodying these concerns improves the quality of pa tient care and reduces exposure to liability for trans fusions with contaminated blood.