Objective: To determine the percentage of children with autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), and combined ASD 1 ADHD who had sleep problems documented by developmental-behavioral pediatricians at diagnostic and follow-up visits at 12 US academic medical centers comprising the Developmental-Behavioral Pediatrics Research Network (DBPNet) and to identify the predictors of sleep problem documentation. Methods: Developmental-behavioral pediatricians completed encounter forms that covered sociodemographic, medical, clinician, and visit factors. There was 1 dependent variable, sleep problem documentation, for which 4 definitions were developed (Model 1 5 Sleep Disorder coded; Model 2 5 Sleep Disorder or polysomnogram coded; Model 3 5 Sleep Disorder, polysomnogram, or sleep medication coded; and Model 4 5 Sleep Disorder, polysomnogram, sleep medication, or clonidine coded). Results: Sleep problem documentation was 14.1% for Model 1, 15.2% for Model 2, 17.3% for Model 3, and 19.7% for Model 4. All values were lower (p < 0.001) than the reported prevalence of sleep problems in these conditions. For Model 4, predictors of sleep problem documentation were age group, ethnicity, medical insurance type, and DBPNet site. Conclusion: Developmental-behavioral pediatricians in DBPNet under-reported sleep problems in children with ASD and ADHD. Variation among sites was substantial. Care plans for children with ASD and ADHD should specify which treating clinician(s) monitors sleep issues.