To ascertain the degree of agreement between a score for screening and another for diagnosis of motor development in 6-month old infants and to define the most appropriate cutoff point for screening.A sectional study, enrolling asymptomatic full term newborns with gestational ages from 37 to 41 weeks, who were discharged from the maternity unit 2 days after birth and are resident in the Campinas area. Infants were excluded if they presented genetic syndromes, malformations, congenital infections, intensive care admission or low birth weight. The assessment instruments investigated were the Alberta Infant Motor Scale (AIMS) and the Bayley Scales of Infant Development II (BSID-II). Two cutoff points were evaluated for the AIMS, the 5th and 10th percentiles, and for the BSID-II infants were classified according to its motor index score (IS) as having inadequate (IS < 85, at least 1 standard deviation below the mean) or adequate performance (IS >or= 85, above the mean minus 1 standard deviation).The study sample comprised 43 infants. Six infants (14.00%) exhibited inadequate motor performance. Using the BSID-II motor classification and the 5th percentile AIMS cutoff, sensitivity was 100%, specificity 78.37%, accuracy 81.39%, kappa index 0.50 and p < 0.001; whereas, using the BSID-II motor classification and the 10th percentile AIMS cutoff, sensitivity was 100%, specificity 48.64%, accuracy 55.81%, kappa index 0.20 and p 0.025.The results suggest that concordance between the two 6-month assessment scales is good. The parameters employed are best combined using the 5th percentile AIMS cutoff point.