To assess the benefits of a new type of hearing aid using cartilage conduction (CC) in patients with severe conduction hearing loss and evaluate its potential for practical use. Consecutive, prospective case series. Forty-one subjects (21 with bilateral aural atresia; 15 with unilateral aural atresia; and 5 others) participated in this study. Fitting and gain adjustments of the CC hearing aids were performed to the ear(s) with conduction hearing loss. The function gains were measured. Evaluation of the measurements of speech performance-intensity functions, speech recognition scores, tolerance of environmental noise, and subject questionnaires were also performed, and judged according to the "Guidelines for the evaluation of hearing aid fitting" established by the Japan Audiological Society. The thresholds were significantly improved by CC hearing aids. The functional gains for CC hearing aids were nearly equivalent to that for their previously used hearing aids. The style of the transducer fixation and the type of aural atresia had no significant influence on the functional gains. Most of the assessment results were judged to be sufficient. Before the trial, bone conduction hearing aids had been used most frequently by bilateral aural atresia subjects. However, after the trial, most subjects continued to use CC hearing aids instead of reverting back to their original device. Overall, 39 subjects continued use of the CC hearing aids. No severe adverse effects were noted in the trial. Cartilage conduction hearing aids could be an additional and beneficial option for severe conduction hearing loss from aural atresia.