Little is known about the current practices of primary care physicians regarding developmental surveillance and screening during pediatric preventive care visits. We conducted a mailed survey of a random national sample of pediatricians and family physicians to describe their practices and identify factors that predict use of developmental screening tools, an efficacious way of identifying children with developmental delays. Most physicians reviewed developmental milestones and prompted parents for developmental concerns at preventive care visits. Approximately half of the physicians used a formal developmental screening instrument. Female physician gender predicted higher rates of use of screening tools for family physicians, but not for pediatricians. Most physicians seemed committed to the early diagnosis of developmental delays. Substantial variability in surveillance and screening practices, barriers of time and reimbursement, and under-reliance on parent-completed questionnaires underscore areas for improvement.