The World Health Organization defines precancerous lesions as morphologically altered tissue in which cancer is more likely to occur than in its apparently normal counterpart. Precancerous condition is a generalized state associated with the significantly increased risk of cancer. Precancerous lesions include leukoplakia, erythroplakia, oral lichen planus and actinic cheilitis, while precancerous conditions include oral submucous fibrosis, lupus erythematosus, PlummerVinson syndrome, syphilis and dyskeratosis congenita. The etiology of these diseases is not yet fully understood. Smoking, alcohol, and local trauma are most commonly reported. The diagnostic tools include a detailed patient history, a clinical examination and a biopsy. Also, the tissue reflectance light visualization technique, fluorescent imaging and vital staining with toluidine can be diagnostically relevant. The treatment consists of conservative drug therapy and surgical removal. The clinical examination of the oral cavity of every patient, regardless of their reason for admission, can help in early precancerous lesion detection, adequate therapy selection and possible oral cancer prevention. This significantly changes the quality of patients’ lives.