HYPOTHESIS: Anomaly in the incudostapedial articulation (IS) may be responsible for persistent conductive hearing loss (HL) in Down's syndrome (DS) patients. Our goal was to perform a detailed histopathologic assessment of the role of the IS joint in the conductive HL. BACKGROUND: In addition to other disabilities, 38% to 78% of patients with Down's syndrome (Trisomy 21) have CHL, some of which are persistent despite maximum treatment. The cause of the persistent conductive HL remains unclear. METHODS: Retrospective analysis of temporal bone histopathology. Analyses of the midsection through the IS joint of 21 temporal bones (13 subjects) patients with DS and 31 temporal bones (18 subjects) from healthy subjects, performed by 2 blinded authors. The length of 7 different parameters of the width of the IS joint was measured and compared between the 2 groups. RESULTS: The IS joint of patients with DS was significantly wider than the normal control. As opposed to the control, it did not decrease because of age. CONCLUSION: The persistent conductive HL in some patients with DS might be caused by anomaly of the IS joint. In severe cases, corrective surgery should be considered.