A follow-up study of a hospital-based population of 166 patients with oral leukoplakia revealed a 2.9% annual malignant transformation rate. The median follow-up period was 29 months. Parameters associated with an increased risk of malignant transformation were female gender (P < 0.025), absence of smoking habits in women (P < 0.05), and a non-homogeneous clinical aspect (P = 0.01). For uniform reporting, a recently proposed classification and staging system has been used. Leukoplakias in stage IV, consisting of lesions with moderate or severe epithelial dysplasia, were associated with an increased risk of malignant transformation (P < 0.01). There were no oral subsites associated with an increased risk. Patients who had any form of intervention did not have a statistically significantly lower chance for malignant transformation than patients who were kept under surveillance without intervention.