ObjectiveTo describe the histopathologic findings within the human cochlea in X‐linked Alport syndrome.Study DesignHistopathologic analysis of cellular elements within the human cochlea by light microscopy.Materials and MethodsA right and a left cochleae of a man with genetically confirmed X‐linked Alport syndrome was studied post‐mortem. The temporal bones underwent standard processing for histologic examination. The slides were examined by light microscopy. Graphic reconstruction of the cochlea was performed to quantify hair cells, pathologic changes of the stria vascularis, and loss of cochlear neuronal cells.ResultsThere was severe loss of inner hair cells and all three rows of outer hair cells in the apical two turns of the cochlea. The stria vascularis and spiral ligament showed areas of marked loss which became more prominent from base to apex in each ear. The spiral ganglion cell count in the Rosenthal's canal exhibited loss of 20% to 45% compared to matched historical controls. There was a zone of separation between the organ of Corti and the basilar membrane extending along the basal surface of Deiters cells, Hensen cells, Claudius cells and external sulcus cells. The tunnel of Corti and the space of Nuel were filled with cellular elements along the cochlea.ConclusionThe histopathologic findings of cochlear involvement in Alport's syndrome are basement membrane separation from the cells of the organ of Corti, outer and inner hair cell loss, and cellular infilling of the tunnel and extracellular spaces of the organ of Corti. These observations contribute to our understanding of the mechanism of sensorineural hearing loss in these patients.Level of Evidence