Objective: To determine the factors causing complications in unilateral total hip replacement. Study Design: Analytical study. Place and Duration of Study: The Aga Khan University Hospital, Karachi, between 2000 and 2010. Methodology: During the study period, 199 patients underwent elective unilateral total hip replacement at the Aga Khan University Hospital. Patients were divided into two groups on the basis of postoperative complications within 30 days of surgery. Significant factors at 5% significance level on univariate analysis were further analyzed by multivariate logistic regression. Results: Postoperative complications occurred in 39 patients (19.6%); dislocation being most common in 13 patients (6.5%), followed by wound infection in four (2%), all of these patients required intervention. Other minor complications which were managed conservatively included wound infection (2.5%), urinary tract infection (2.5%), dislocation (1%), pleural effusion and pneumonia (2%), deep venous thrombosis (0.5%) and myocardial infarction (0.5%). On univariate analysis, patients with ASA III and IV, peri-operative blood transfusion, pre-operative hip deformity and post-operative bisphosphonate use were significantly associated with complications. On multi-variate analysis, adjusted odd\u27s ratio for perioperative transfusion (3; 95% CI: 1.17-7.7) and hip deformity (3.2, 95% CI: 1.4-3.4) was found statistically significant. Conclusion: Pre-operative hip deformity and perioperative blood transfusion significantly influence the rates of complication after unilateral THR
