Ganglia around the proximal tibiofibular joint usually occur within the synovial membrane, tendon sheath, or peroneal nerve, but rarely within muscle. A 30 year old male had a painless lump over the lateral aspect of a leg, weakness of dorsiflexion of the ankle and diminution of sensation on the dorsum of the foot, which was suspected to be peroneal compartment syndrome. We experienced a case of an intramuscular ganglion that developed in the peroneus longus and brevis muscle mimicking peroneal compartment syndrome which was satisfactorily treated by excision.