A retrospective review of dengue patients admitted to Queen Sirikit National Institute of Child Health (previously known as Children's Hospital) from 1995 to 1999 revealed 4,532 confirmed cases of dengue infection; 80.9% were dengue hemorrhagic fever (DHF) and 19.1% were dengue fever cases (DF). Among the DHF patients; 30.6% had shock. The majority of them, 66.6%, had a normal nutritional status, while 9.3% were malnourished and 24.2% had obesity as classified by weight for age. Compared with control patients with other diagnoses (excluding HIV/AIDS patients), malnourished children had a lower risk of contracting dengue infection (odds ratio = 0.48, 95% Cl = 0.39-0.60, p = 0.000) while obese children had a greater risk of infection with dengue viruses (odds ratio = 1.96, 95% Cl = 1.55-2.5, p = 0.000). The clinical signs, symptoms and laboratory findings of dengue were almost the same among the 3 groups of malnourished, normal, and obese patients. The minor differences observed were that in obese children liver enlargement was found less often; maculopapular/convalescence rash and elevations of alanine aminotransferase were found more often. Malnourished patients had a higher risk of developing shock (37.8%) than normal (29.9%) and obese patients (30.2%) (p = 0.000). Obese patients had more unusual presentations: encephalopathy (1.3%) and associated infections (4.8%), than normal (0.5% and 2.7%) and malnourished patients (1.2% and 3.1%). Complications of fluid overload were found more in obese patients (6.5%) compared to normal (3.2%) and malnourished patients (2.1%) (p = 0.000). The case-fatality rates (CFR) in malnourished patients and obese patients were 0.5% and 0.4%, respectively, while in normal patients the CFR was 0.07%. Under and over nutrition DHF patients had either a greater risk of shock or unusual presentations and complications, which can lead to severe disease or complications and probably a higher CFR.