To review the factors that result in skin ulceration of patients with chronic venous insufficiency. Data sources:Index Medicus was searched using an on-line computer system for years 1966–1995 to identify articles relating to venous ulceration and the microcirculation. Data extraction: Articles and sections of articles relating to the mechanisms which cause venous ulceration and the efficacy of the treatment of venous ulceration have been included. Data synthesis: It seems unlikely that venous ulceration is attributable to failure of diffusion of oxygen and other small nutritional molecules to the tissues of the skin. It is much more likely that neutrophils attach themselves to the cutaneous microcirculation, become activated and produce endothelial injury. Repeated over many months or years, this leads to the chronic inflammatory process of lipodermatosclerosis. The microvascular changes in the skin are characterised by activated endothelium and perivascular inflammatory cells. Conclusion: There is evidence of leucocyte involvement in the pathogenesis of venous ulceration. The exact mechanisms remain to be resolved. Improved treatment for patients may be devised with a better understanding of the basic causes of this condition.