OBJECTIVE: In a previous study the authors found that dendritic spine density was reduced on prefrontal pyramidal neurons in layer 3 of subjects with schizophrenia. From a neural circuitry perspective, understanding the pathophysiological significance of this finding requires knowledge of whether pyramidal neurons in other cortical layers are similarly affected. The authors’ goal was to determine whether their finding in layer 3 was also present in other cortical layers in the same group of subjects with schizophrenia. METHOD: Spine density and other dendritic measures were made for pyramidal neurons in layers 5 and 6 of prefrontal area 46 in the brains of deceased subjects with schizophrenia, subjects with other psychiatric disorders, and normal comparison subjects. RESULTS: None of the dendritic measures for layer 5 or 6 pyramidal neurons differed across the subject groups, but the within-subject differences in spine density between deep layer 3 and layer 5 or 6 pyramidal neurons were significantly greater in the patients with schizophrenia than in the comparison subjects. CONCLUSIONS: These findings are consistent with the idea that prefrontal pyramidal neurons involved in corticocortical and/or thalamocortical connections are preferentially affected in schizophrenia.