Rett syndrome (RTT) is often associated with Autism, Cerebral Palsy It is often misdiagnosed as palsy or nonspecific developmental delay. There is a simple blood test to confirm the presence of the MECP2 mutation; however, since we know that the MECP2 mutation is also seen in other disorders, the presence of the MECP2 mutation is not sufficient for the diagnosis of Rett Syndrome.

Diagnosis requires the presence of a mutation (molecular diagnosis) or the fulfillment of diagnostic criteria (a clinical diagnosis based on observed signs and symptoms), or both. A list of diagnostic criteria is provided below.