Aim: The aim of this study was to characterize the auditory brainstem responses (ABRs) of young children with suspected autism spectrum disorders (ASDs) and compare them with the ABRs of children with language delay and with clinical norms. Method: The ABRs of 26 children with suspected ASDs (21 males, five females; mean age 32.5 mo) and an age- and sex-matched group of 26 children with language delay (22 males, four females) were analysed. All children had normal hearing. The absolute latencies of waves I, III, and V, and interpeak latencies (IPLs) I to III, I to V, and III to V of the group with ASDs and the group with language delay were compared. Data from both groups were further compared with clinical norms. Results: All absolute latencies and IPLs were significantly prolonged in the group with suspected ASDs compared with the group with language delay, excluding IPL III-V (all "p"-values less than 0.05) and with clinical norms (all "p"-values less than 0.001; IPL III-V, p less than 0.05). Significant prolongation of absolute and IPLs was also evident in the group with language delay compared with clinical norms, excluding IPL III to V (all "p"-values less than 0.001). The prevalence of abnormal findings in two or more absolute latencies was found to be significantly higher in the group with ASDs (50%) than in the group with language delay (8%; p = 0.002). Interpretation: The results provide first-time evidence for a neurodevelopmental brainstem abnormality that is already apparent in young children with suspected ASD and language delay. The overlap in ABR findings supports the assertion that an auditory processing deficit may be at the core of these two disorders.