Typical features of Ankylosing spondylitis are progressive ankylosis of the sacroiliac joint and ossification of the annulus fibrosus of discs, interlaminar & interspinous ligaments. Fixed kyphotic deformity in ankylosing spondylitis causes many problems, such as difficulty in looking forward, gastrointestinal problems, restricted cardiopulmonary functions and psychotic depression. There are limitations of conservative treatment to delay progression of the disease. So surgical osteotomy for the correction is inevitable. Osteotomy is indicated in poor horizontal vision, poor cardiopulmonary & gastrointestinal function and psychological & social problem. The purpose of this study is to assess the results of posterior closed wedge osteotomy in ankylosed kyphotic deformity. The posterior closed wedge osteotomy was performed for 30 patients in ankylosed kyphotic deformity between April 1995 and February 1997, who were 29 male and 1 female and whose average age at the time of operation was 35.7 years (17-54 yrs). Mean duration of the symptoms was 18 years (11-23 yrs). The level of correction was fully evaluated preoperatively with anterior and lateral radiographs of whole spine. The patient was placed pronely on an operating table which could be angulated in reverse direction. The determined correction level of the spine was exposed through the posterior midline approach. Following the insertion of pedicle screws, transpedicular decancellation was performed with curret and punch forceps. Posterior bony element and pedicle were completely removed. The correction was achieved by gradual extension of the operating table angulated previously and by opposing the surface of osteotomy. Then prebent rod was applied. Walking brace was applied in 2 weeks postoperatively. The osteotomy was performed at single level in 28 cases, double level in 2 cases. The level of osteotomy was distributed as follows; T10: 1 case, T12: 1 case, L2: 3 cases, L3: 14 cases, and L4: 13 cases. Mean correction angle was 48.7degrees (13degrees-72degrees ), and mean increment of height 13.7cm (4-23.5cm). There was no fatal complication. But 5 patients had paralytic ileus and 3 patients visual loss; one was permanent, the others were temporary. Temporary neurologic deficit was also noted in 5 cases. Posterior closed wedge osteotomy with transpedicular decancellation in ankylosed kyphotic deformity is relatively safe and simple procedure.