PURPOSE: The purpose of this study was to identify the relationship between the common peroneal nerve (CPN) and the fibular head. METHODS: Sixteen cadaveric dissections were performed. The distance from the fibular head to the center of the CPN as it exits beneath the biceps femoris (BF) was measured in 0°, 30°, 60°, and 90° of flexion and was averaged on the first 8 specimens. Based on those measurements, a needle was placed on the second 8 dissections before the fascial incision was made to assess reliability. All measurements were repeated after needle removal, distances were recorded, and 95% confidence interval (CI) and correlation coefficients were calculated. RESULTS: The distance from the posterior border of the fibular head to where the CPN nerve center emerges from the BF was 62.3 mm (95% confidence interval [CI], 58.2 to 66.4), 56.3 mm (95% CI, 51.9 to 60.8), 46.8 mm (95% CI, 43.6 to 50.0), and 45.3 mm (95% CI, 43.2 to 47.3) in 0°, 30°, 60°, and 90° of knee flexion, respectively. The correlation coefficient between knee flexion and measured distance was nearly linear: r = -0.97. The correlation coefficients were 0.62, 0.32, and 0.01 for height, weight, and body mass index (BMI), respectively. The CPN crossed the posterior border of the fibula 21.9 mm (95% CI, 20.2 to 23.7) from the fibular styloid at 90° of flexion. CONCLUSIONS: With the knee in 90° of flexion, the CPN center crosses the long head of the BF (LHBF) tendon 45.3 mm from the posterior border of the fibula, where the direct arm of the BF inserts, and the posterior border of the fibula 21.9 mm from the tip of the fibular styloid. There is a near linear correlation between knee flexion and the distance to the CPN as it exits the BF. No correlation exists between the distance to the CPN and weight or BMI, whereas a moderate correlation with height exists. CLINICAL RELEVANCE: These relationships allow for efficient and safe identification of the CPN proximal to the zone of injury when operating around the posterior lateral corner (PLC) of the knee.