The purpose of this study was to investigate cement leakage (CL) in osteoporotic vertebral compression fractures (OVCFs) with cortical defect using high-viscosity bone cement during unilateral percutaneous kyphoplasty (PKP) surgery.This study included a series of 77 patients (23 males, 54 females) with single level osteoporotic vertebral body fracture (OVCF) who underwent unilateral PKP in our hospital. Preoperative x-ray, computed tomography (CT) scan, and 3-dimensional reconstructions were studied. During the PKP procedure, needle was carefully put to avoid too near to the cortical defect according to CT image. High-viscosity bone cement was used via unilateral PKP. Radiographic outcomes were evaluated by assessment of vertebral body wall breakage, fracture type, and vertebral body change. The exact rate of CL was analyzed.A total of 77 patients with single-level OVCF were included in this study. The mean age of the patients was 74.8 ± 8.0 years. Among these cases, 7 (9.1%) involved the thoracic spine (T3-T10), 60 (77.9%) involved the thoracolumbar spine (T10-L2), and 10 (13.0%) involved the lumbar spine (L3-L5). There were 27 vertebral bodies found posterior wall breakage, 51 vertebral bodies found endplate breakage, and 49 vertebral bodies found anterior-lateral wall breakage. CT scan was more efficient in detecting vertebral body wall breakage and CL than x-ray (P < .001). No neurological symptoms were found after surgery. Both cases with CL (CL group) and cases without cement leakage (NCL group) experienced vertebral height restoration (HR) with similar cement volume CV. There were no significant difference between the two groups about the parameter HR and CV. Severe vertebral body fracture and biconcave fracture had more CL than other groups. OVCF cases with cortical defect had more CL rate than those without cortical defect; however, no significant difference was found in the correlation between vertebral wall breakage and CL.Cortical defect remains a potential risk of CL during PKP surgery. Careful preoperative evaluation and using high-viscosity bone cement during the unilateral PKP procedure could prevent serious leakage and clinical symptoms.