To assess immunization practices and attitudes of U.S. primary care physicians regarding adult influenza and pneumococcal immunizations. 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. 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 <65 years with chronic disease indications with both influenza and pneumococcal vaccine. Reported barriers for influenza vaccination included vaccine safety concerns by patients (58%), urgent concerns dominating visits (43%), and inadequate reimbursement (26%). Reported barriers for pneumococcal vaccination included urgent concerns during office visits (44%), no patient immunization history (36%), patient concerns about vaccine safety (31%), and inadequate reimbursement (25%). Many physicians indicated willingness to try tracking systems (72%), chart reminders (55%), patient reminders (53%), standing orders (36%), external lists of unimmunized patients for pneumococcal vaccination (74%), external patient reminders (70%), and office training of physicians (36%) or staff (46%). While most physicians favored adult vaccinations, practical barriers to vaccination exist. Most physicians would adopt evidence-based strategies to improve immunization delivery.