Often in the clinic, I am asked by many elderly patients with knee pain, “Do I have synovitis?” It is as if synovitis is a very scary and difficult disease. Synovitis is a multifaceted disease characterized by synovial exudation, joint swelling, and pain. It occurs mainly in the knee joint, which is the largest and most complex of all joints in the body, and also the joint with the largest synovial area. Fundamentally, synovitis is a general term for swollen joints until a definitive diagnosis is made. There are many causes of joint swelling, such as bleeding and oozing due to trauma; infections of the joint, such as septic arthritis and tuberculosis; osteoarthritis and rheumatoid arthritis; and gout, among others. Therefore, synovitis is rarely diagnosed clinically, unless the cause cannot be determined and a certain type of joint swelling is diagnosed palliatively as synovitis. In the elderly, in the absence of obvious trauma, the vast majority of joint swelling has a definite cause, which is osteoarthritis or rheumatoid arthritis. Therefore, do not assume that it is synovitis as soon as joint swelling occurs. Instead, you should visit a regular hospital to determine the diagnosis and give the appropriate treatment.