This report presents a new parent-rated outcome measure of insomnia for children with autism spectrum disorder. Parents of 1185 children with autism spectrum disorder (aged 3-12; 80.3% male) completed the first draft of the measure online. Factor and item response theory analyses reduced the set of 40 items to the final 21-item Pediatric Insomnia Autism Rating Scale. In this online sample, Pediatric Insomnia Autism Rating Scale mean was 21.8 ± 15.0 (range 0-63; coefficient alpha = 0.94). Item response theory results indicated excellent reliability across a range of scores. Next, we conducted a telehealth assessment of 134 children with autism spectrum disorder (aged 3-12; 73% male). In this clinical sample, Pediatric Insomnia Autism Rating Scale mean was 28.9 + 14.62 (range 0-61; coefficient alpha = 0.93). Pearson correlations of Pediatric Insomnia Autism Rating Scale with the PROMIS Sleep Disturbance and the modified Children's Sleep Habits Questionnaire was 0.74 for each. This was significantly higher than correlations of parent-rated disruptive behavior, hyperactivity, repetitive behavior, and anxiety measures (range 0.29-0.59)--supporting convergent and divergent validity. Parents of 63 children completed the Pediatric Insomnia Autism Rating Scale three times over 4 weeks. Intraclass correlation was excellent (0.88) over three time points. Pediatric Insomnia Autism Rating Scale is a valid dimensional measure of insomnia in autistic children that produces reliable scores.