The purpose of this study is to learn more about risk factors for autism by studying the behavior and brain functioning of toddlers with early communication delays and typically developing toddlers. Children 12 or 18 months of age with language delays (i.e., no words at 18 months, limited vocalizations at 12 months) and typically developing toddlers may be eligible to participate. This study will be conducted at the NIH Clinical Center in Bethesda, Maryland. There will be an initial screening evaluation that will include behavioral assessment. Eligible participants will then complete a baseline visit that includes an overnight sleep study that includes Electroencephalogram (EEG) test to measure brain electrical activity, and an MRI scan. Follow-up visits that include behavioral assessment will occur every 6-12 months, depending on age at study entry. The final study visit will occur at 36 months of age and will include behavioral assessment, sleep/EEG study, and MRI. There is no cost for participation. Compensation will be provided. To find out if your child qualifies or for more information, please call 301-451-7822 (TTY: 1-866-411-1010) or e-mail NIMH-ASD@mail.nih.gov. National Institute of Mental Health, National Institutes of Health, Department of Health & Human Services....