Employers and health plan directors would like to know whether it is cost-effective to include outpatient nutrition services as a covered benefit. The purpose of this systematic review was to examine the strength of evidence on the cost-effectiveness of outpatient nutrition services from an economic perspective. All randomized controlled trials published between January 1966 and September 2001 that reported on costs and effectiveness of outpatient nutrition services for any indicated condition were identified and reviewed. Paired reviewers abstracted data from and assessed the quality of each eligible randomized controlled trial; 13 studies met the eligibility criteria. Relatively consistent evidence exists to support the cost-effectiveness of nutrition services in the reduction of serum cholesterol levels (eg, 20 dollars to 1,268 dollars per mmol/L decrease in serum low-density lipoprotein level), weight loss (2.40 dollars to 10 dollars per pound lost), and blood glucose (5 dollars per mmol/L decrease), and for target populations with diabetes mellitus and hypercholesterolemia. However, the randomized controlled trials had important limitations and used different cost perspectives. Limited evidence of economic benefit exists to support coverage of outpatient nutrition services for selected indications. More randomized controlled trials of nutrition services should be conducted, taking into consideration all potential candidates for nutrition therapy and all potential costs to patients, providers, and payers.