i was told one leg swelling can be from arthritis, blood clot in that leg, insufficient circulation and heart issues......My mother has it in one leg. Her knee is really swollen on that leg too bec she has bad arthritis in it , they told her to drink more water, get off caffeine and sodas, to get more exercise...at least 400 steps a day instead of laying around, hence swelling can be from kidneys as well from water retention which is really bad....good diet, avoid salt and bad fats etc....more fruits and vegatables....