Case: A 21-year-old college soccer player suffered from knee joint pain, but neither preoperative clinical examination nor magnetic resonance imaging could detect a precise diagnosis. Arthroscopy showed that medial meniscus hypermobility led to impingement of the femorotibial joint surface. After inside-to-outside meniscus suture, the abnormal hypermobility could no longer be observed. The player returned to sports without any previously experienced symptoms. Conclusions: We present a case report of the hypermobile medial meniscus without substantial tear treated by meniscal suture. A careful arthroscopy inspection was the key element of the diagnosis and subsequent successful surgical treatment.