For over 50 years, there has been uncertainty in the conceptual understanding and neuropathogenesis of the diagnosis of schizoaffective disorder (SCA). In order to better characterize SCA, we performed a quantitative assessment of MRI neuroanatomical structures in patients with SCA (n = 12), compared to patients with bipolar disorder (BPD) (n = 12) and healthy volunteers (HV) (n = 12). Patients diagnosed with SCA exhibited regional abnormalities on the striatum that resemble those seen in BPD. This study suggests that SCA has some neuroanatomical characteristics similar to BPD.