Heterozygous mutations in the WFS1 gene are responsible for autosomal dominant low frequency hearing loss at the DFNA6/14 locus, while homozygous or compound heterozygous mutations underlie Wolfram syndrome. In this study we examine expression of wolframin, the WFS1-gene product, in mouse inner ear at different developmental stages using immunohistochemistry and in situ hybridization. Both techniques showed compatible results and indicated a clear expression in different cell types of the inner ear. Although there were observable developmental differences, no differences in staining pattern or gradients of expression were observed between the basal and apical parts of the cochlea. Double immunostaining with an endoplasmic reticulum marker confirmed that wolframin localizes to this organelle. A remarkable similarity was observed between cells expressing wolframin and the presence of canalicular reticulum, a specialized form of endoplasmic reticulum. The canalicular reticulum is believed to be involved in the transcellular movements of ions, an important process in the physiology of the inner ear. Although there is nothing currently known about the function of wolframin, our results suggest that it may play a role in inner ear ion homeostasis as maintained by the canalicular reticulum.Keywords WFS1 · Inner ear · Immunohistochemistry · In situ hybridization · Canalicular reticulum Recessive mutations in the WFS1 gene also cause Wolfram syndrome, known by the acronym DIDMOAD to reflect the syndrome phenotype of diabetes insipidus, diabetes mellitus, optic atrophy, and deafness (Inoue et al. 1998;Strom et al. 1998). In contrast to the low frequency K. Cryns and S. Thys contributed equally K. Cryns · S. Thys · L. Van Laer · G. Van Camp ( ) )