The young child with fever represents a diagnostic challenge. The physician has powerful allies with which to meet this challenge--the carefully performed observation, history, and physical examination. This evaluation, along with an appreciation of age and temperature risk factors, can lead to optimum patient care and to a more apposite use of both screening and diagnostic laboratory studies. Decisions about hospitalization and therapy are based on an appreciation of causative agents, a comprehensive knowledge of disease processes, and any aspects of the social situation that could have an adverse influence on outpatient management.