The Autism Diagnostic Interview—Revised is one of the “gold standard” diagnostic tools for autism spectrum disorders. It is traditionally administered face-to-face. Cost and geographical concerns constrain the employment of the ADI-R for large-scale research projects. The telephone interview is a reasonable alternative, but has not yet been examined for reliability with face-to-face administration. In this study, participants were interviewed both face-to-face and on the telephone using the complete ADI-R interview. Results indicate that there was no significant difference between the algorithm scores or the diagnoses arrived at for face-to-face and telephone administrations. Reliability statistics across the two modalities were very good and indicate that telephone interviews using the ADI-R are a viable option for researchers.