An apparently normal early development was one of the initial criteria for classical Rett syndrome. However, several investigators considered Rett syndrome to be a developmental disorder manifesting very soon after birth. Videos of 14 infants with Rett disorder were carefully assessed for their spontaneous movements, in particular general movements (GMs), during the first 4 months of life. A detailed analysis clearly demonstrated that none of the infants had normal GMs. However, a specific abnormal GM pattern could not be detected for Rett disorder. The abnormal GMs described here, and their individual developmental trajectories are different from the abnormal GMs described in infants with acquired brain lesion. Our study is the first to apply specific standardised measures of early spontaneous movements to infants with Rett syndrome, proving conclusively that the disorder is manifest within the first weeks of life.