Objective: Describe the psychomotor development (PMD) in upper middle class children, utilizing Bayley's Scale of Intellectual Development (BSID), internationally standarized. Patients and Methods: A total of 119 children in groups of 8, 18 and 30 months were enrolled at the well-baby clinic in a Private Hospital in Santiago, Chile. BSID III was utilized in all cases. Children born preterm, or with neurological, genetic, or metabolic diseases were excluded. Results: BSID scores followed a normal distribution (100.3 ± 10). Prevalence of déficit was found to be 30%) at 8 months, 7.7%> at 18 months, and 2.7%> at 30 months, without gender difference. Gross motor development and language predominated at 8 months. Ther threee subscales showed an upward trend, cognitive and motor scales most significantly. Gross motor scales, which had been deficient at 8 months became normal at 18 months. Conclusions: The high frequency of motor deficits found at 8 months of age was striking. While all scales improved, cognitive and motor scales were most significant. The effect of stimulation and upbringing patterns upon chil development is discussed, being important for future studies of causality.