Epidermal inclusion cyst is a common mass in life. It is covered with a stratified squamous epithelium, thus, there is a granular cell layer adjacent to the keratin-containing cyst lumen. It can be caused by mechanical force, trauma, or a spontaneous event. It can rupture spontaneously or be ruptured by external mechanical forces. Epidermal inclusion cysts that exhibit inflammation or recur should be removed by simple excision. In this case, the patient showed an epidermal inclusion cyst under an anterolateral thigh free flap, which can cause the palpable mass to go unnoticed. First we thought he had neuroma formation after a surgical procedure on his foot. However it was an epidermal inclusion cyst, which was diagnosed by a special pathologist. It is a curious and rare case.