The lack of sensitive measures suitable for use across the range of functioning in autism spectrum disorder (ASD) is a barrier to treatment development and monitoring. The Emotion Dysregulation Inventory (EDI) is a caregiver-report questionnaire designed to capture emotional distress and problems with emotion regulation in both minimally verbal and verbal individuals. The first two phases of the EDI's development are described, including: (1) utilizing methods from the Patient-Reported Outcomes Measurement Information System (PROMIS®) project to develop the item pool and response options; and (2) assessment of the EDI in psychiatric inpatients with ASD. The results suggest that the EDI captures a wide range of emotion dysregulation, is sensitive to change, and is not biased by verbal or intellectual ability.