Abnormal neurodevelopment in midline structures such as the adhesio interthalamica (AI) has been reported in schizophrenia, but not consistently replicated. We investigated the prevalence and anterior-posterior length of the AI in 62 schizophrenia patients (32 males, 30 females) and 63 healthy controls (35 males, 28 females) using magnetic resonance imaging. We also explored the relation between the AI and volumetric measurements for the third ventricle, medial temporal structures (amygdala, hippocampus, and parahippocampal gyrus), superior temporal sub-regions, and frontal lobe regions (prefrontal area and anterior cingulate gyrus). The AI was absent in 24.2% (15/62) of the schizophrenia patients and in 9.5% (6/63) of the controls, showing a significant group difference. For the length of the AI, schizophrenia patients had a shorter AI than controls, and males had a shorter AI than females. The subjects without an AI had a significantly larger third ventricle and smaller parahippocampal gyrus than the subjects with an AI for both groups. We found a significant diagnosis-by-AI interaction for the amygdala. The schizophrenia patients without an AI had a smaller bilateral amygdala than those with an AI, whereas the AI was not associated with the volume of the amygdala in the control subjects. These findings suggest that the absence of AI in schizophrenia could be a marker of developmental abnormalities in the neural network including the thalamus and connected amygdaloid regions, which may play an important role in the pathogenesis of schizophrenia.