Lipoma arborescens (LA) is a rare lesion that causes joint effusion and pain. LA usually presents as a unilateral knee lesion, and bilateral lesions are extremely rare. LA among adolescent patients is also extremely rare with the disorder having a much higher incidence among adults. This paper reports a 14-year-old boy who was treated for bilateral knee LA. X-rays revealed the characteristic features of LA in both knees, and arthroscopic synovectomy was performed to resect the lesions. Postoperative recovery progressed smoothly, and the patient was eventually relieved of pain and swelling. LA should be considered when adolescent patients present with bilateral pain and swelling, even though this condition is rare in this age group. Furthermore, surgical synovectomy for a complete resection is an appropriate treatment option.