Conclusion: The facial recess approach is preferred in common cavity (CC) malformation with an incomplete basal turn, and the transmastoid single-slit labyrinthotomy approach in classic CC malformation. Patients with CC benefit from cochlear implantation (CI) over time, but the audiological and speech development is poorer than in cases with normal cochleas. Objectives: To discuss the surgical aspects and performance of CI in 21 patients with CC malformation. Methods: Twenty-one CC malformations were classified into 2 types: classic CC malformation and CC malformation with an incomplete basal turn. Twenty-one patients without inner ear malformation were set as the control group. Thus, data for 42 patients were analyzed. Results: The facial recess approach was used in 3 patients with CC malformation with an incomplete basal turn, and the transmastoid single-slit labyrinthotomy approach in 18 patients with classic CC malformation. After follow-up for 36 months, the average free-field hearing threshold was higher, and the scores for the CAP, SIR, IT-MAIS, and closed-set/open-set auditory speech perception tests were lower than in the control group (p < 0.05).