We have studied 25 cases of squamous cell carcinoma in chronic venous leg ulcers. Twenty-three of the patients were dead and two were alive. The mean age at cancer diagnosis was 78.5 years. The median survival was 1 year. Eleven tumours were well-differentiated, 10 moderately and four poorly. All patients with a poorly differentiated tumour died within a year. Metastases were certain in eight cases. The disease was lethal in 10 cases which included all poorly differentiated tumours. The survival of the study group was significantly shortened compared with a control group of patients with lower limb non-melanoma skin cancer (n = 433) from the Swedish Cancer Registry (P = 0.0084). When diagnosed, squamous cell carcinoma in chronic leg ulcers merits a thorough investigation of the degree of differentiation and spread. Assertive treatment is indicated as poorly differentiated tumours and some moderately differentiated tumours may be fatal.