This study explores the relationship between cognitive, motor, social and personality development of 3-year-old children and the age of their entry into preschool, which ranged from 10 to 45 months. 247 children from 17 preschools in different regions of Slovenia, all implementing the same National Curriculum, participated. Preschool teachers assessed the social behaviour of the participating children on the Social Competence and Behaviour Evaluation Scale. Individual child personality differences were rated independently by their mothers and fathers, and by their preschool teachers using a recently developed culturally- and age-decentred Inventory of Children's Individual Differences. The Bayley Scales of Infant Development-II were individually administered to each child, providing an evaluation of the child's mental and motor developmental status and the child's behaviour during the application of the Mental and Motor Scales. Groups of children who entered preschool at different ages (10 to 15 months, 16 to 30 months and 31 to 45 months) and came from different educational backgrounds (low, middle or high parental education) were compared with respect to the above indicators of their development, while controlling for the quality of parental care (stimulation, affection and demandingness). The results suggest that early entry per se does not present a risk factor for later developmental problems, however, it is associated with sociability, assertiveness and absence of internalising problems. Furthermore, parental educational level is linked to several of the children's personality traits as perceived by their care givers (mothers, fathers and teachers), mostly to those representing the cognitive aspect of personality, although the differences in parental educational level are not reflected in the children's actual performance on the Mental Developmental Scale. (Contains 3 figures.)