AbstractAn anatomical study of the formation of the sural nerve (SN) was carried out on 76 Thai cadavers. The results revealed that 67.1% of the SNs were formed by the union of the medial sural cutaneous nerve (MSCN) and the lateral sural cutaneous nerve (LSCN); the MSCN and LSCN are branches of the tibial and the common fibular (peroneal) nerves, respectively. The site of union was variable: 5.9% in the popliteal fossa, 1.9% in the middle third of the leg, 66.7% in the lower third of the leg, and 25.5% at or just below the ankle. One SN (0.7%) was formed by the union of the MSCN and a different branch of the common fibular nerve, running parallel and medial to but not connecting with the LSCN, which joined the MSCN in the lower third of the leg. The remaining 32.2% of the SNs were a direct continuation of the MSCN. The SNs ranged from 6–30 cm (mean = 14.41 cm) in length with a range in diameter of 3.5–3.8 mm (mean = 3.61 mm), and were easily located 1–1.5 cm posterior to the posterior border of the lateral malleolus. The LSCNs were 15–32 cm long (mean = 22.48 cm) with a diameter between 2.7–3.4 mm (mean = 3.22 mm); the MSCNs were 17–31 cm long (mean = 20.42 cm) with a diameter between 2.3–2.5 mm (mean = 2.41 mm). Clinically, the SN is widely used for both diagnostic (biopsy and nerve conduction velocity studies) and therapeutic purposes (nerve grafting) and the LSCN is used for a sensate free flap; thus, a detailed knowledge of the anatomy of the SN and its contributing nerves are important in carrying out these and other procedures. Clin. Anat. 15:263–266, 2002. © 2002 Wiley‐Liss, Inc.