Intraosseus ganglion cysts are uncommon, benign, juxta-articular and usually found within long bones. A 35-year-old male presented with acute right ankle pain. He denied any traumatic event. Tenderness was localized on the subtalar joint. Radiologic studies demonstrated a cystic lesion in the juxta-articular portion of the posterior facet of the calcaneus. The patient underwent excision and curettage. Postoperative recovery was uneventful. A histological examination confirmed a typical intraosseus ganglion cyst. A case of an intraosseus ganglion cyst of the calcaneus causing acute subtalar joint pain is described.