The fibularis longus, also referred to as the peroneus longus, is a muscle inside the outer area of the human leg, which everts (bends in an outward direction) and flexes the ankle.

The muscle is attached to the head of the fibula and is controlled by the fibular nerve. It runs the length of the fibula and eventually turns into a tendon at the lateral malleolus (the bony projection at the outer edge of the ankle). It stretches to the underside of the foot and attaches to the first metatarsal and the medial cuneiform bones. The fibularis longus works in conjunction with the tendons of the peroneal retinaculum to help to stabilize the leg on top of the foot. Blood flow to this muscle is provided by the fibular artery.