OBJECTIVE In analyzing data from a larger study, we noticed significant disagreement between results of 2 commonly used developmental screening tools (Parents' Evaluation of Developmental Status [PEDS; parent concern questionnaire] and Ages & Stages Questionnaires [ASQ; parent report of developmental skills]) delivered to children at the same visit in primary care. The screens have favorable reported psychometric properties and can be efficient to use in practice; however, there is little comparative information about the relative performance of these tools in primary care. We sought to describe the agreement between the 2 screens in this setting. METHODS Parents of 60 children aged 9 to 31 months completed PEDS and ASQ screens at the same visit. Concordance (PEDS and ASQ results agree) and discordance (results differ) for the 2 screens were determined. RESULTS The mean age of children was 17.6 months, 77% received Medicaid, and 50% of parents had a high school education or less. Overall, 37% failed the PEDS and 27% failed the ASQ. Thirty-one children passed (52%) both screens; 9 (15%) failed both; and 20 (33%) failed 1 but not the other (13 PEDS and 7 ASQ). Agreement between the 2 screening tests was only fair, statistically no different from agreement by chance. CONCLUSIONS There was substantial discordance between PEDS and ASQ developmental screens. Although these are preliminary data, clinicians need to be aware that in implementing revised American Academy of Pediatrics screening guidelines, the choice of screening instrument may affect which children are likely to be identified for additional evaluation.