The technique of decision analysis was used to compare the benefits (prevention of major infectious sequelae of bacteremia) and risks (unnecessary hospitalization and intravenous antibiotic treatment of children whose bacteremia would have resolved spontaneously, discomfort of venipuncture) of alternative diagnostic management strategies in the evaluation of children 3 to 24 months of age with fever (rectal temperature greater than or equal to 39 degrees C) of acute (less than or equal to 4 days) onset and without evident focus of bacterial infection. The diagnostic strategies compared at the initial visit were blood culture in all, blood culture in none, and selective blood culture (restricted to children judged to be at high risk). Probability estimates were based on published epidemiologic studies and case series, and utilities were elicited from mothers of 3- to 24-month-old children and from pediatricians. Based on initial probabilities and utilities, the "no blood culture" strategy had the highest expected utility, followed closely by the "selective blood culture" strategy, with the "blood culture all" strategy a distant third. Sensitivity analyses based on increased risk of major infectious sequelae or of bacteremia had no effect on the ranking of the three initial management options. Eliminating the "disutility" of venipuncture or augmenting the disutility of major infectious sequelae also failed to alter the ranking. Even when an extreme relative disutility for major sequelae was assumed, the "blood culture all" strategy was not favored. Thus, the risk of unnecessary hospitalization and intravenous antibiotic treatment of the relatively large number of children whose bacteremia spontaneously resolves appears to outweigh the benefit of preventing serious infectious sequelae in the few children in whom positive blood culture results permit timely intervention. The explicitness and coherence of the decision analysis approach should help in developing a rational diagnostic approach to the young febrile child.