One hundred children admitted to a hospital over a six-year period with temperatures over 38.5 C for longer than two weeks and of undetermined etiology are reviewed. Fifty-two were infectious (21 presumed viral), 20 collagen-inflammatory, 6 malignancy, 10 miscellaneous, and 12 discharged undiagnosed. Children less than 6 years were more likely to have an infectious etiology while 80% of collagen-inflammatory disease occurred in the group older than 6. The overall mortality (9%) was not age-related. Careful history and physical examinations were helpful but the usual laboratory data (CBC, urinalysis, X-ray) were notably disappointing; however, sedimentation rates and serum protein electrophoresis were often reliable screening tests. Biopsy and laparotomy were less frequently done but when performed yielded productive information. Unusual presentations of common diseases comprised the majority of childhood fevers.