We report a Delphi Consensus modification and first validation study of the Autism Diagnostic Observation Schedule -- 2 with deaf children and young people (ADOS-2 Deaf adaptation). Validation included 122 deaf participants (aged 2-18 years), 63 with an Autism Spectrum Disorder (ASD). This was compared to a National Institute for Health and Clinical Excellence (NICE) guideline standard clinical assessment by blinded independent specialist clinicians. Results showed overall sensitivity 73% (95%CI 60%, 83%); specificity 71% (95%CI 58%, 82%), and for the more common modules 1-3 (combined as in previous studies) sensitivity 79% (95% CI 65-89%); specificity 79% (95% CI 66-89%) suggesting this instrument will be a helpful addition for use with deaf children and young people.