Deep Vein Thrombosis (DVT): This is often the first consideration for unilateral peripheral oedema due to its relatively high prevalence and the potential for serious complications like pulmonary embolism. DVT typically presents with swelling, pain, and warmth in one leg.

Cellulitis: A bacterial infection of the skin and subcutaneous tissues that can cause unilateral oedema, redness, warmth, and pain. It's a common condition that can mimic other serious diseases.
Lymphedema: This condition results from impaired lymphatic drainage, leading to chronic swelling. It can be primary (inherited) or secondary (due to surgery, infection, or trauma).
Venous Insufficiency: Includes conditions like varicose veins and post-thrombotic syndrome, where the veins have problems returning blood to the heart, leading to swelling, usually in the legs.

Compartment Syndrome: A serious condition resulting from increased pressure within a muscle compartment, which can lead to muscle and nerve damage. It's characterized by the "5 Ps": pain, pallor, pulselessness, paresthesia, and poikilothermia.
Phlegmasia Cerulea Dolens: A severe form of DVT that causes significant swelling and cyanosis of the affected limb, potentially leading to gangrene.
Malignancy: Certain cancers, like lymphoma or tumors compressing lymphatic or venous vessels, can cause unilateral oedema.

Filariasis: A parasitic infection that can cause lymphedema, typically seen in tropical regions.
Fabry Disease: A genetic disorder that can lead to lymphedema and other systemic symptoms due to the accumulation of a particular type of fat in the body's cells.
Klippel-Trenaunay Syndrome: A rare congenital condition characterized by port-wine stains, varicose veins, and bony and soft tissue hypertrophy, leading to unilateral oedema.