Major depression is a common comorbidity in autism spectrum disorder (ASD), often difficult to identify and to treat. Autistic subjects are more at risk for suicidal thoughts and behaviors compared to typically developing peers. Unfortunately, ASD individuals are more frequently treatment-resistant and often show side-effects which reduce efficacy. Intranasal esketamine has been recently approved as an add-on medication for treatment-resistant depression (TRD), but it has never been used in ASD with comorbid major depression. Of note, a pilot study of intranasal ketamine has shown no effect on social withdrawal in ASD without depression. The present case report describes the first girl with ASD and comorbid TRD treated with intranasal esketamine.