An ideal way to assess the effectiveness of femoropopliteal bypass procedures is to standardize patient- and surgeon-related variables by randomization. Through statistical analysis of multiple factors influencing patency, limb loss, death rate and hospital stay, the authors reviewed retrospectively 136 bypass procedures performed over 5 years. Variables that contributed significantly to the results were: preoperative symptoms (p = 0.037), graft material used (p = 0.016), age of the patient (p = 0.007), adequacy of runoff (p = 0.041) and smoking postoperatively (p = 0.013). Autogenous vein grafts were superior to prosthetic grafts, the cumulative patency at 5 years being 67.5% and 38.2% respectively. The authors emphasize that all patients needing vascular surgery should be advised to stop smoking, since in this study postoperative smoking increased the probability of limb loss and adversely affected the cumulative patency rate by interaction with other variables such as preoperative symptoms, graft material and age.