The Multicenter Study of the Natural History of HIV Infection in Hemophilic Children (also titled, for brevity's sake, the Hemophilia Growth and Development Study - HGDS) consists of 1) a network of 14 clinical centers for patient recruitment and a 4-year follow-up, and 2) a data coordinating center for computer and logistical support, forms development, and data entry and limited periodic analyses. The object of the study is to monitor and compare the health of three cohorts of children: HIV-infected hemophiliacs, non-infected hemophiliacs, and non-hemophiliac, non-infected male siblings of hemophiliacs. For each study participant a comprehensive data base of medical history and health events will be put together, with emphasis on the prospective collection of data on body growth, and endocrine and neuropsychological development. At the conclusion of the second year of operation (May 1988 - April 1990), the data coordination center for HGDS (New England Research Institute, Inc.) has participated in the finalization of the study design, the standardization of protocols and forms for data flow, recruitment, baseline, follow-up and laboratory examinations, and the continued training of clinic personnel who participate in the study. By the end of April, 1990, 263 patients had been enrolled and evaluated.