Extreme prematurity is known as a risk factor for autism spectrum disorder (ASD). However, the association between prematurity and ASD, for children born moderately and late preterm (MLPT) and those born early term (ET), is less established. This retrospective study aimed to characterize the phenotypic characteristics (i.e. behavioral profile and cognitive abilities) of 254 children with ASD, between 3 and 15 years of age, born MLPT (19 children), ET (60 children) and full term (175 children). MLPT and ET births do not modify ASD symptomatology, but modify cognitive development. The results highlight that incomplete gestation, i.e., MLPT or ET, has a negative impact on both verbal and nonverbal cognitive abilities, in children with neurodevelopmental vulnerability.