Summary We have given a brief summary of the scale of the problem caused by venous ulceration in the UK, and have then reviewed the various theories of causation, including a historical survey, and presented the evidence for and against the two main current theories of fibrin cuffs and white cell trapping. We also outline previous hypotheses of the aetiology of venous ulceration, including arteriovenous microanastomoses, stasis and oedema. The contribution of superficial venous incompetence in the pathogenesis of ulceration is also examined.