The authors describe the cases of two patients with chronic venous stasis ulcers, in which squamous cell carcinoma developed. They stress that chronic venous ulceration is one facultative pre-cancerous condition, i.e. one of a number of chronic processes that provide a basis from which carcinoma may develop over a period of years or decades. Skin tumors, especially squamous cell carcinoma, may arise under the conditions of chronic inflammatory processes (crural ulcers, lichen sclerosus et atrophicus, acrodermatitis chronica atrophicans) or chronic degenerative changes (sclerotic scars or atrophies). According to the literatuře, squamous cell carcinoma develops in 1/5000 cases of venous stasis ulcers; based on experience, the authors suggest that it is likely to be more frequent.

        Key words: chronic venous stasis ulcer, facultative precanceroses, squamous cell carcinoma.