INTRODUCTION: We found a spontaneous fusion at adjacent vertebrae after percutaneous vertebroplasty (PVP) or kyphoplasty in osteoporotic compression fractures and analyze the radiologic & clinical characteristics. MATERIALS & METHODS: Between January 2000 and December 2011, 555 patients were treated with PVP or kyphoplasty for osteoporotic compression fracture in our department. We classified the spontaneous fusion as two groups. One is solid spontaneous fusion group with at least three cortical continuity to adjacent vertebrae, the other is partially fusion group which progressed fusion compared to previous radiologic finding. We reviewed the plain film and analyzed the radiologic characteristics of those patients with duration of fusion, location and extent of fused segments. A clinical characteristic by visual analogue score (VAS) compared to our previous report was checked. RESULTS: Among them, 54 patients (9.7%) had an solid spontaneous fusion and 43 patients (7.7%) had partially fused on plane image. In solid fusion group, the average duration of fusion was 19 months ranged of 3 to 48 months. Forty six cases (85%) of solid fusion patients had occurred with proximal adjacent vertebrae and 7 cases (13%) had proximal with distal adjacent vertebrae. Forty one cases (76%) of spontaneous fusion occurred within 1 segment and 13 cases within multiple segments. The most cases of solid fusion group were occurred at thoracolumbar junction (40 patients, 74%). Mean VAS score of solid fusion group was 2.0 at final follow-up and were analyzed relatively low score compared to mean VAS of our previous report (2.0, 2.8 respectively). CONCLUSION: After percutaneous vertebroplasty or kyphoplasty in osteoporotic compression fracture, unpredictable spontaneous fusion could develop more than 10% rate, especially with proximal vertebra within 1 segment at thoracolumbar junction in radiologic aspect. Clinically, patients with spontaneous fusion had a tendency of more reduced pain than others.