Despite the importance of expressive language for individuals with autism spectrum disorder (ASD), expressive language assessments are not consistently included in ASD research and many studies do not adequately describe participants' verbal abilities. A valid and efficient measure of expressive language would facilitate consistent reporting across ASD research studies and provide data for additional analyses. The current study developed a new Autism Diagnostic Observation Schedule (ADOS-2) expressive language score and examined convergent and divergent validity in a large, well-defined sample of children with ASD. This score was highly correlated with other measures of expressive language (including parent-report, direct assessment, and clinician ratings) and less strongly correlated with measures of receptive language and nonverbal cognitive ability, providing good evidence of convergent and divergent validity.