Background: Rubinstein-Taybi syndrome (RSTS) is a multiple congenital anomaly syndrome characterised by several typical somatic characteristics and by developmental disabilities with various degrees of severity. Focusing on children with RSTS, the aim of this study was to describe their psychomotor, cognitive, and socio-emotional developmental profiles. Method: Twenty-three children with RSTS (12 boys; 11 girls; mean chronological age: 4 years and 10 months) with severe intellectual disability (mean developmental quotient = 32.39) were recruited from an Expert Department of Medical Genetics. Developmental assessments were carried out with the Brunet-Lézine-Revised scale and the Social Cognitive Evaluation Battery. Results: The participants' developmental profiles were characterised by heterogeneous psychomotor development, homogeneous cognitive and socio-emotional development, by more severe delays in expressive language, vocal imitation, and symbolic play skills, and by better developmental levels in socio-emotional abilities. Conclusions: Based on these atypical developmental profiles, early interventions should target the three most delayed abilities.