Many physicians use surveillance questions to assess development; the American Academy of Pediatrics recommends screening at 9-, 18-, and 24-month health supervision visits (HSVs). There are no studies directly comparing surveillance with screening. The authors directly compared systematic surveillance with standardized screening using a cross-sectional observational study of children with no known delays. Surveillance questions were completed at each HSV. The Ages and Stages Questionnaire (ASQ) was administered following the 9-, 18-, or 24-month HSV. The authors compared detection of delays by surveillance with ASQ screening. Using surveillance, 11/95 subjects were identified as delayed. Using the ASQ, 15/95 subjects scored fail; 28/95 scored monitor. Among the 11 delayed surveillance subjects, 5 scored fail on the ASQ and 5 scored monitor. Ten of the 15 subjects scoring fail on the ASQ were not identified by surveillance. The study's findings support the American Academy of Pediatrics recommendations for periodic formal screening in addition to continued surveillance.