Lipid profile was evaluated prospectively in 23 consecutive children, aged 3.2-14.9 years, admitted to the hospital with a febrile illness (pneumonia, upper respiratory tract infection, diarrhea, pyelonephritis, mononucleosis, appendicitis). The degree of dyslipidemia associated with fever was assessed using each child as his/her own control and by comparison with 93 non-febrile children who had no evidence of fever during the past six months. Total cholesterol decreased during the symptomatic phase of the disease. The magnitude and duration of its decrease appeared to be related to the degree and duration of fever. Low HDL-cholesterol and hypertriglyceridemia were observed during the late stage of the febrile disease and were still detected in the convalescent phase. This study suggests that in children, transient and sometimes prolonged lipid changes may occur in association with an infectious febrile disease. This effect is important for defining the appropriate timing for screening for dyslipidemias.