We report the very rare case of an 8-year-old boy who accidentally fell on the ground, causing the lead of a pencil to penetrate his left knee joint cavity. After radiographic diagnosis, the pencil was removed by a physician at a private clinic and the boy was referred to our department for further evaluation. We performed arthroscopic retrieval of the pencil lead through standard arthroscopic portals without an accessory portal. Postoperatively, the patient had a quick recovery without problematic sequelae.