The clinical distinction between autism spectrum disorders (ASD), also called pervasive developmental disorders (PDD), and schizophrenia is often difficult to make. Here we describe a case of an adult patient presenting with a diagnosis of schizophrenia based on a history of functional deterioration and presumed persecutory delusions. A psychiatric and psychological assessment conducted from a developmental perspective, in association with direct observation and neuropsychological evaluation for intellectual disabilities and autism, led to a diagnosis of PDD not otherwise specified, with revision of the initial diagnosis of schizophrenia.