After the initial description of acquired immunodeficiency syndrome (AIDS) in Romania in late 1989, national AIDS case surveillance was established with a modified version of the World Health Organisation (WHO) clinical case definition. This modified case definition requires that AIDS cases have both clinical and serological evidence of human immunodeficiency virus (HIV) infection. Before December, 1989, Romania had reported 13 AIDS cases to WHO. By Dec 31, 1990, 1168 AIDS cases were reported to Romania's Ministry of Health, of which 1094 (93.7%) occurred in children less than 13 years of age at diagnosis. Of these, 1086 (99.3%) were in infants and children less than 4 years of age, and 683 (62.4%) in abandoned children living in public institutions at the time of diagnosis. By Dec 31, 1990, 493 (45.1%) mothers of children with AIDS had been located and tested, and 37 (7.5%) were positive for HIV; 423 (38.7%) cases were in children who had received transfusions of unscreened blood, and 6 (0.5%) were in children with clotting disorders. HIV transmission through the improper use of needles and syringes is strongly suspected in most of the remaining 628 (57.4%) children with AIDS, most of whom had received multiple therapeutic injections. This outbreak demonstrates the serious potential for HIV transmission in medical facilities that intensively and improperly use parenteral therapy and have poor sterilisation technique.