Autism is a diagnosis characterized by social and communication impairments. Onset of autism occurs before the age of 3. However, there can be delays in identification, diagnosis, and treatment. A number of symptoms of autism overlap with other childhood mental health disorders, often accounting for a delay in correct diagnosis. The following case highlights how a high-functioning female child with autism was misdiagnosed as having depression at a relatively late age. Clinicians with high-functioning child clients, who appear to have a flat affect and social isolation, are advised to be aware of the possibility of autism in such presentations. Issues around differentiating the diagnosis between depression and autism in children will be discussed, along with assessment and treatment of this particular case.