Chronic Venous Insufficiency: This condition is a common cause of bilateral leg swelling due to the inability of veins to return blood to the heart properly, leading to fluid accumulation in the legs.

Heart Failure: Bilateral leg swelling can be a sign of heart failure, where the heart is unable to pump enough blood, leading to fluid buildup in the body, particularly in the legs.
Nephrotic Syndrome: A condition characterized by excessive loss of protein in the urine, leading to low albumin levels, which can cause fluid to leak out of blood vessels and accumulate in the legs.
Liver Cirrhosis: Cirrhosis can lead to fluid retention and swelling in the legs due to portal hypertension and hypoalbuminemia.
Hypothyroidism: Although less common, hypothyroidism can cause swelling in the legs due to fluid retention and decreased lymphatic drainage.

Deep Vein Thrombosis (DVT): A potentially life-threatening condition where a blood clot forms in the deep veins of the legs, which can lead to pulmonary embolism if the clot breaks loose.
Lymphoma: Certain types of lymphoma can cause swelling in the legs due to obstruction of lymphatic vessels.
Sepsis: In severe cases, sepsis can cause fluid to leak out of blood vessels, leading to swelling in the legs.

Lipedema: A rare condition characterized by the abnormal growth of fat cells in the legs, leading to swelling and pain.
Fabry Disease: A genetic disorder that can cause swelling in the legs due to the accumulation of a particular type of fat in the body's cells.
Milroy Disease: A rare condition that affects the lymphatic system, leading to swelling in the legs due to impaired lymphatic drainage.