Despite the fact that the pedicled gastrocnemius flap has been used clinically for almost two decades, precise data on its neurovascular anatomy are lacking. A detailed knowledge of the neurovascular anatomy of this flap may encourage its more extensive use as a donor site by the means of microvascular free-tissue transfer. The femoral or popliteal artery in 27 fresh cadavers was injected with radiopaque contrast material to study the gross vascular supply of 54 medical and 50 lateral gastrocnemius muscles. The intramuscular vascular anatomy also was analyzed in 29 medial and 24 lateral gastrocnemius muscles using x-ray technique. Depending on the number of the sural arteries that supply the gastrocnemius muscle, flaps were classified as type 1 or type 2. Type 1 muscle bellies (lateral or medial gastrocnemius muscle belly) are supplied by one sural artery, while in type 2 muscles two arteries supply one muscle belly. Eighty-five percent of medial and 84 percent of lateral gastrocnemius muscle bellies had single vascular pedicles (type 1). The point of origin of the sural artery(s) permitted us to further classify the blood supply to the muscle bellies as subtypes A, B, and C. Intramuscular vascular anatomy is characterized as either a single vessel (dominant type) or two vessels (nondominant type). A single motor nerve, from the tibial nerve, accompanied the primary vascular pedicle into each muscle belly. When there were two vascular pedicles supplying one muscle belly, only one motor nerve accompanied the major pedicle.(ABSTRACT TRUNCATED AT 250 WORDS)