The NRC (National Research Council) task force on head and neck cancer issued this document to help clinicians involved in diagnosing and treating precancerous oral diseases. Chapter 1 includes definition, epidemiology, risk factors (alcohol, smoking, poor oral hygiene), WHO classification, clinical picture of leukoplakias, erythroplasia, lichen planus, as well as their natural history. Chapter 2 points out the clinical signs to be looked for in order to make a proper diagnosis and discusses biopsy techniques. Chapter 3 deals with therapeutic procedures (surgical technique and medical treatment), while Chapter 4 concerns follow-up according to the clinical and histological diagnosis. Finally, some statistical forms are enclosed: Form 1 consists of information regarding educational qualifications, occupation, alcohol consumption, smoking and dietary habits; Form 2 consists of information about previous diseases and the history of the present disease; Form 3 records the signs and symptoms observed for the precancerous lesion; Form 4 records treatment modalities; Form 5 records patient follow-up.