Some of the causes for swelling in only one leg include:
Infection in the foot or leg
Muscle strain or tear in the affected leg
Blockage of the leg's lymphatic system
A Baker's cyst (located behind the knee)
Long-term problem with a vein not working well (venous insufficiency)
Swollen, twisted vein in the leg (varicose veins)
Insect bite or sting on the foot or leg
Injury or recent surgery on the foot or leg
Blood clot in a deep vein of the leg (deep vein thrombosis or DVT)
Inflammation of the joints of the lower leg
Follow these guidelines when caring for yourself at home:
Don’t wear tight clothing.
Keep your legs up while lying or sitting.
Take any medicines as directed.
If infection, injury, or recent surgery is the cause of your swelling, stay off your legs as much as possible until your symptoms get better.
If you have venous insufficiency or varicose veins, don’t sit or stand in one place for long periods of time. Take breaks and walk around every few hours. Talk with your healthcare provider about wearing support stockings to help reduce swelling during the day.
Wear compression stockings with your provider's approval.