This chapter focuses on the neurodevelopmental basis of diagnostic overlap and symptom commonality by addressing similarities and differences in the neuroanatomical and functional neurochemical basis of three common childhood/adolescent-onset neuropsychiatric disorders: attention-deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), and mood disorder, including major depressive disorder (MDD) and bipolar disorder (BPD). These disorders are selected because of the clinical commonalities with schizophrenia and because of the known or presumed developmental origins of these disorders. Schizophrenia, BPD, and OCD have their onset in adolescence or early adulthood, and they may be preceded by symptoms similar to those in developmental disorders such as ADHD. The disorders are discussed in comparison with schizophrenia. The chapter describes the relevant findings in schizophrenia. It limits the pathophysiological discussion to the neuroimaging findings, and considers common genetic and environmental etiologic factors that may cut across these disorders.