Unexplained swelling of lateral side of right ankle?

Many possibilities : This could be something that is bony, tendinous or ligamentous in nature. I recommend that you see an orthopedic foot and ankle surgeon for diagnosis or treatment. One in your area can be found at www.Aofas.Org.

Is there pain?: You could have an ankle sprain, you could have a tear in a peroneal tendon, or tenosynovitis of one. The could be excess fat tissue that you think is swelling. Knowing if there was pain and when it hurts would help.