Synovial chondromatosis presented as knocking sensation of the knee in a 14-year-old girl.

Knee joint is the most common site of synovial chondromatosis with the prevalence in middle-aged male. The following is the description of a 14-year-old girl presented with a knocking sensation during the motion of her joint, which is a less common occurrence at her age. Loose bodies in the left knee joint were excised as much as possible with arthroscopy. The patient was asymptomatic when moving her knee after arthroscopic synovialectomy and removal of the loose bodies. In spite of the less possibility of malignant transformation of synovial chondromatosis, long-term follow-up is still recommended in this 14-year-old girl due to the supposed genetic abnormalities.