Infant temperament is a constitutional characteristic which shows high to moderate stability. It is recognized as a useful tool with which to address infant's relationship to his environment, specially in the mother-infant interaction and nursery process. The main objective of the study was to evaluate the relation between the mother's perception of infant's temperament at 6 months and PMD at 12 months. A prospective field trial was carried out in Santiago, Chile, which enrolled 1101 infants belonging to low and middle-low socioeconomic families. All were healthy children, birthweight >3000 gr without perinatal, genetic and/or neurologic illness. Infant temperament was assessed through the Bates Questionnaire (ICQ), and the PMD using the Bayley Scales. Results show that mothers reported difficulties in caring for their infants. They perceived them as Difficult (17.5%), Unpredictable (23.6%), Unadaptable (33.2%) and Dull (36.4%). High scores in Dullness factor were associated with lower Mental development Index (p<0.01) and lower Motor Development Index (p<0.0001). The Easy + Dull temperamental combination represented a higher risk for PMD, and Difficult + Unpredictable children reached the highest development indexes. We conclude that the concept of infant temperament is a useful tool for parent counseling with regard to PMD and for early prevention of high risk infants.