The study focuses on language and cognitive abilities of siblings of the linguistically most affected children with autism (i.e. siblings of nonverbal children - SIBS-ANV). Twenty-eight SIBS-ANV (17 boys), ages 4-9 years, took part in the study. All children attended regular schools, and none had received a diagnosis of autism. Controls were 27 typically developing children (SIBS-TD; 16 boys) matched to the SIBS-ANV on age, family background, socioeconomic status and type of school they attended. Significant IQ differences, as well as language differences as measured on the Clinical Evaluation of Language Fundamentals (CELF), emerged between SIBS-ANV and SIBS-TD. However, differences in the language scores mostly disappeared when PIQ and FSIQ were controlled for. Furthermore, grammatical analysis of spontaneous speech samples produced in the course of testing did not reveal any significant differences between the groups. These results add to recent work suggesting that language deficits may not be part of the Broad Autism Phenotype (BAP). It further suggests that the cognitive deficit characteristic of nonverbal people with autism may be familial.