In the present study, language performance on standardized assessments (e.g., overall verbal performance, receptive and expressive vocabulary) and spontaneous language produced in play was compared between preschool-aged boys with autism spectrum disorder ([subscript n]ASD, n = 25) and boys with fragile X syndrome (FXS, n = 16). At the group-level, we observed weaknesses in the language skills of boys with [subscript n]ASD relative to those with FXS (e.g., when considering raw score performance, standard score performance relative to nonverbal cognitive skills, frequency of talk in play), after controlling for nonverbal IQ and ASD symptom severity. Moreover, although individually most children in both groups demonstrated language delays relative to CA-expectations, language delays relative to nonverbal level-expectations were more common in boys with [subscript n]ASD.