This study compared family and professional assessments of the communication skills of 34 preschool males with fragile X syndrome. Parents and professionals rated the boys' receptive and expressive communication. Parents also reported on the vocabulary skills of 16 of the boys, whereas professionals assessed their vocabulary diversity using a communication sample. Moderate agreement was found between parents and professionals for expressive communication ratings, whereas agreement for receptive communication ratings was low to moderate. Parents rated their children significantly higher than professionals for receptive communication but not for expressive communication. Parents and professionals rated children at a higher cognitive age as having fewer difficulties with receptive and expressive communication, whereas older children were rated as having more problems.