A report of 19 cases of serologically-proven dengue hemorrhagic fever (DHF) in infants aged 3-12 months who were admitted to the Department of Pediatrics, Chon Buri Regional Hospital, Thailand, during 1995 to 1998. Subjects were 8 males and 11 females, with the peak age of 8 months. Four cases (21%) had DHF and other common co-infections ie pneumonia (2 cases), Staphylococcus aureus sepsis (1 case) and Haemophilus influenzae meningitis (1 case). The clinical manifestations of the 15 DHF cases were high fever (100%), coryza (93.3%), hepatomegaly (80%), drowsiness (53.3 %), and vomiting (46.7%); rash was observed in only 27%; one-fifth developed febrile convulsions. Sites of bleeding were the skin (petechiae) 58%, gastrointestinal system (melena) 16%, and mucous membrane (epistaxis) 5%; thrombocytopenia and increased hematocrit >> or =20%) were noted in 95% and 84% respectively. The majority of the patients (18 cases, 95%) had primary infection; only one (5%) had secondary infection. The clinical severity of the DHF was Grade I, II, and III (dengue shock syndrome) in 21%, 47% and 32% of cases respectively. After appropriate and effective management, all the infants recovered fully.