All forms of chronic leg ulcer have a risk of undergoing malignant transformation and squamous cell carcinoma is the most common type. Known as Marjolin’s ulcers, they have a high metastatic potential and their prognosis is poor if they are not detected at an early stage. In this article the authors outline the pathophysiology of these ulcers as well as presenting features, detection and treatment methods. They conclude that healthcare professionals should monitor any chronic non-healing ulcers that do not respond to treatment very carefully and consider an early biopsy to assess for cancerous degeneration.