Validation of a Parent Completed Developmental Screening Questionnaire Introduction: Psychomotor Development (PMD) is an essential component of health care. Several authors have attempted to facilitate this evaluation through quick and inexpensive tools that do not prolong the time of consult. The "Ages and Stages Questionnaire" (ASQ) is a well-known and validated parentdirected survey. Objective: To evaluate the psychometric validity of ASQ, through comparison with Bayley's Scale of Infant Development (BSID), a universally accepted tool which measures similar parameters, and is administered by an expert. Patients and Methods: Children seen at an upper-middle class Private Clinic in Santiago, Chile were admitted to this study, with the exception of pre-term newborns, or children with known neurological, genetic or metabolic disease. Groups were formed at 8, 18 and 30 months of age. A sample of nearly 40 children per age Group was formed. After parents responded to the ASQ, an expert, blind to the results of the ASQ, evaluated each patient within two weeks. Results: Total number of children enrolled was 119. PMD deficit was scored in 19.3% of children according to ASQ, 14.3% according to BSID (not significant). While the results obtained with both tests were found to be correlated (r = 0.52), scores obtained through BSID were lower among children with deficit, compared to those rated through ASQ (p < 0.001). The sensitivity of ASQ was 58.8% and the specificity was 87.2%. Conclusions: Both tests are correlated. ASQ was found to be highly specific, suggesting its use as a screening tool in outpatient clinics, at least in a similar a population. These results should be reevaluated after national validation, to determine cutting points and test potency in all populations.