At what age do children with Williams syndrome (WS) achieve major developmental milestones? Is their early development harmonious or are some of the typical discrepancies described in older children already noticeable? To address these questions we analysed information gathered over a five year period on 14 children with WS. Each child was evaluated at least twice between the ages of 5 and 48 months, using the Bayley Scales of Infant Development and during more informal observation sessions. Parents and professionals were also interviewed. This analysis provided us with an outline for "developmental norms" for children with WS and allowed us to conclude that, even before the age of 4 years, children with WS display a typical profile in their abilities. Expressive language skills are less delayed in contrast to the important delay in language comprehension and fine motor skills.