The present study investigated the language development of 50 children with intellectual disabilities (ID) and 42 typically developing children from age 4 to 5 years, and was designed to shed more light on the respective roles of phonological working memory (WM) and nonverbal intelligence in vocabulary and syntax development. Results showed that nonverbal intelligence predicted phonological WM, vocabulary and syntax of children with ID at age 4 and 5, and that it only predicted these skills at age 4 in typically developing children. Furthermore, syntax at age 5 was predicted by vocabulary at age 4 in children with ID, which points to children with ID requiring a larger critical mass of vocabulary for syntactic development to be initiated. (Contains 2 figures and 3 tables.)