Congenital agenesis of the stapes and the oval window is rare. Congenital stapedial agenesis (CSA) may be recognized preoperatively in the presence of conductive hearing loss. The principal radiological imaging approach of the temporal bone, computed tomography (CT), can be used to diagnose CSA. Our 17-year-old male patient (case A) had long-term hearing loss which was getting worse. A temporal bone CT scan revealed the absence of the stapes and the oval window on both sides and an abnormal position of the facial nerve. No anomalies were detected in the external ear structures. Explorative right ear tympanotomy revealed an abnormal inferior course and dehiscence of the facial nerve. The oval window and stapedial structures were absent. Patients were evaluated for continued hearing aid use or bone-anchored hearing aid implantation. Similar CT imaging and clinical abnormalities were seen in his 16-year-old sister (case B). They did not have any other siblings and neither of their parents nor any of their relatives had hearing loss. This report presents the CT scans of the two siblings with mixed hearing loss (mainly conductive) and the perioperative image of the first case. A genetic study may help explain the etiopathogenesis since both cases had similar clinical and imaging findings.