Three hundred cases of cranioplasty, following large decompressive craniectomy for various diseases, were analyzed. 1. Neurological status was evaluated before and after cranioplasty in 52 patients with remaining neurological deficit. There observed no changes in 13 patients with skin flap of full or bulging type. However, 4 (10%) among 39 patients with skin flap of sinking or flat type showed unquestionable objective improvement within a few days following cranioplasty, after stationary period of more than 2 and half months. In these situation, placement of acrylic plate has presumably corrected deformity of underlying brain tissue secondary to pressure gradient between extra- and intracranial spaces, which might have unidentifiably caused unfavorable eflects on neural function. 2. Seven children underwent procedure within 24 months of age and all of them had troublesome bluging of skin flap. This deformity was extreme in 5, in whom the dura mater was not repaired in the previous surgery. Those children had various intracranial problems as causes of bulging skin flap-hydrocephaly in 2, porencephaly in 1, CSF collection under the skin flap in 4, brain migration in 2, enlarged subarachnoid space over the bulging brain surface in 2, deformity of the skull resembling growing skull fracture in 5; and as complications of cranioplasty in 3 and infection in 2. 3. Fracture of the cranioplasty was seen in 7 (2%) among 300 cases and 6 of them were under the age of 7. In one case, there occurred 3 episodes of fracture. 4. Infected cranioplasty, in all as epidural empyema, was seen in 10 (3%) of 300 cases. One of the most important factors related to infection, was the time interval after the primary surgery; all infected cases were operated on within 3 months.