Objective: This study is to describe surgical morphological types of the crista fenestra (CF) in relation to round window membrane (RWM) and to determine its impact on cochlear implant (CI) via the RW insertion. Conclusion: In spite of large morphological diversity, Crist Fenestra can be classified into two main types. Most of them were no need for its removal whereas in a minority of the cases it hinders electrode insertion and needs drilling. KEYWORDS: Cochlear implant, round window membrane, Crista fenestra, drilling.