Background: Given the importance of adaptive behaviour (AB) for the identification of intellectual disability and the design of intervention plans for people with Down syndrome (DS), this cross-sectional study explored AB in infants with DS, compared to infants with typical development (TD). Method: we evaluated 60 infants (10-36 months) with ABAS-II (32 with DS, 28 with TD). Using the developmental trajectories method for data analysis, we compared AB between the two groups. Results: We found significant differences between groups in most of the skills assessed, in favour of infants with TD. Three different patterns of trajectories were found for the AB and the relation between the groups: (1) no differences (Leisure and Self-Care Skills); (2) differences at the beginning of the trajectory and then a similar slope (Home Living, Self-Direction, Social and Motor Skills); and (3) a similar starting-point with differences in the trajectories (Communication, Community Use, Pre-Academic, and Health and Safety). Conclusions: This empirical cross-sectional study contributes to the understanding of the development of AB in children with DS, showing both weak areas and skills that continue improving over time in these early years. Contributions and limitations of the study are discussed.