Parent reports such as MacArthur-Bates Communicative Development Inventories (CDIs) have been suggested as a measure of language in young children with autism since this group often score below base levels of direct tests. However, questions have been raised concerning the reliability of report-based assessments. Parents and preschool teachers filled out the CDI-Words & Gestures for 55 children diagnosed with autistic disorder. Inter-rater reliability analyses were done for the whole sample and a subgroup of minimally verbal children (n = 28). Further, potential over- or under-estimation, comparing the raters was analyzed. Results suggested excellent to fair inter-rater reliability between parent and preschool teacher. Parents tended to rate the children slightly higher than preschool teachers. However, the differences were small, and most likely due to contextual variations. These findings suggest that parents can be reliable sources of information about language abilities in children with autism. Therefore, when children are difficult to assess through direct tests, parent reports such as the CDI can be a good alternative. (author abstract)