Objectives. To assess immunization practices and attitudes of U.S. primary care physicians regarding adult influenza and pneumococcal immunizations.Methods. Mailed survey of primary care internists and family physicians across the United States; four follow-up contacts by mail and telephone. Bivariate and multivariate analyses assessed immunization practices and attitudes and differences by physician characteristics.Results. Three hundred and sixteen of 668 eligible physicians responded (50 refused, response rate of 266 = 40%); 220 provided adult vaccinations. More than 64% indicated they routinely vaccinated patients >=65 years and those Conclusions. While most physicians favored adult vaccinations, practical barriers to vaccination exist. Most physicians would adopt evidence-based strategies to improve immunization delivery.