Growth mechanism of hollow crystals of II-VI compounds is summarized. Hollow ZnO crystals grown by oxidizing ZnSe in the vapour phase are classified into four types: (1) A needle-type hollow crystal is composed of a cluster of c-whiskers. (a) A hollow crystal growing at the top of a long substrate crystal is formed by a combination of the top and normal branch crystals which are composed of c-whisker cluster. (3) A hopper-type hollow crystal is formed by a combination of several top branch crystals grown on short substrate crystals. (4) Twinned hollow crystals with a composition plane (1122) or (1011) are also composed of a cluster of c-whiskers. On the other hand, hollow CdSe and CdS crystals with many striations parallel to the c direction on their side surface were obtained by the sublimation method. Proposed growth mechanisms for these hollow crystals are as follows: (1) Hollow CdSe crystals are composed of many c-needles grown on the lateral surface of an initial c-needle. The c-needles are developed from c-whiskers. These c-needles are united into a wall, leaving a cavity at its center. (2) Hollow CdS crystals are grown by a combination of several Crystal walls extending from previously grown walls. Each wall is developed from an array of c-whiskers. As the result of such combination of crystal walls Several cavities are left in the crystal.