Interventions that utilize academic detailing to improve childhood immunization have been implemented across the country. This study evaluates the effectiveness of an academic detailing intervention to increase childhood immunization rates in pediatric and family medicine practices in a major metropolitan area. Educational teams of one physician, nurse, and office manager delivered 83 peer education sessions at practices in the intervention group. Postintervention immunization rates for children 12-23 months of age increased 1% in the intervention group and decreased 3% in the control group. Postintervention coverage levels for children 12-23 months of age did not differ between the intervention and control groups. Results indicated this office-based intervention was not sufficient to effect measurable changes in immunization coverage levels after 1 year of participation. Future interventions need to provide initial feedback regarding practice immunization coverage levels prior to the educational interventions and include multiple encounters.