At the Hospital Nacional de Niños of Costa Rica, we have studied 14.023 hemocomponent transfusion in a twelve month (from April 1992 to April 1993), we intend to clasifity any transfusion reaction in hemolytic and not hemolytic. We studied 14.023 transfusion and we detected 45 transfusion reaction: We classified it according to sex, age, hemocomponent, amount, type and clinical signs, the follow up protocol allow us to put them as cases of anti paltelets, anti HLA cases, IgA deficiency or red blood cells related.