PURPOSE: To evaluate the effect of the tourniquet on intraoperative patellar tracking and to determine how this may influence the decision to perform lateral release during primary total knee arthroplasty (TKA). MATERIALS AND METHODS: From Jan. 1998 to Feb. 1999, 126 TKAs in which patellar tracking was assesed with tourniquet inflated were chosen as a control group. From May 1999 to June 2000, a total of 221 consecutive TKAs in which patellar tracking was assessed before and after tourniquet release were selected as a study group and were placed into 1 of 3 groups: Group I (49 out of 221) were knees that tracked properly both before and after tourniquet release. Group II (150 out of 221) were knees that maltracked with the tourniquet inflated and subsequently corrected with the tourniquet deflated. Group III (22 out of 221) were knees that maltracked both before and after tourniquet release, therefore required a lateral release. The lateral release rate, patella tilt and displacement were compared among groups. RESULTS: In control group, the lateral release rate was 65.9%(83/126). The patella tilit and displacemen were 2.65+/-0.78 degree and 3.51+/-1.68 mm respectively. In study group, the lateral release rate was 10.0%(22/221). The patella tilit and displacement were 0.76+/-0.85degree and 2.96+/-1.96 mm in study group. CONCLUSION: Tourniquet application alters intraoperative patellar tracking during TKA. When contemplating lateral retinacular release, tourniquet release and reevaluation of patellar tracking should be considered.