OBJECTIVE To compare pre-operative characteristics and peri-operative findings in patients undergoing unilateral total knee arthroplasty (UTKA) and simultaneous bilateral total knee arthroplasty (BTKA). To work out safety criterion for selection of patients for simultaneous BTKA. METHODS Patients undergoing UTKA (39) and BTKA (36) in Department of Orthopaedic Surgery, Combined Military Hospital, Rawalpindi from March 2014 to August 2014 were compared in terms of patient characteristics, underlying pathology, peri-operative blood loss, transfusion requirements and in hospital complications. RESULTS The mean age of patients undergoing UTKA was 61±11 years and those undergoing BTKA was 64±8 years, with similar male to female ratio (1:1.8) in both groups. Males undergoing BTKA were significantly older than other patients (71±6 years). Primary osteoarthritis was the most common initial diagnosis (59% in UTKA and 89% in BTKA, p<0.05) followed by rheumatoid arthritis. Average blood loss per knee was higher in BTKA procedures but difference did not reach statistical significance. Blood transfusion requirements in BTKA patients not receiving antifibrinolytic agent were significantly higher than in similar UTKA patients (75% vs 17%, p<0.05) but were significantly reduced with peri-operative administration of antifibrolytic therapy (30% BTKA, p<0.05). Complication rates, low in both, were more frequent in BTKA patients with co-morbidities. CONCLUSIONS In patients requiring bilateral knee replacements, staged total knee replacement [i.e. the two knees are replaced with a gap of at least 3 months] is a safe approach. Unilateral knee replacement is associated with lesser complications and blood transfusion requirements as compared to simultaneous bilateral total knee replacements.