The aim was to clinically study the frequency and extension of the melanin pigmentation in the attached gingiva and its relation to tobacco smoking. The population examined consisted of patients and dental nurse students at the School of Dentistry in Umeå, Sweden. All of the patients with pigmentation proved to be tobacco smokers. The pigmentation was given to name "smokers' melanosis.". Between 12.9% and 14.9% of those examined and between 25.5% and 31.0% of those who smoked had smokers' melanosis. Patients with smokers' melanosis had a significantly higher tobacco consumption than smokers without pigmentation. In 95.2%, smokers' melanosis was found in the mandible and was most common in the attached gingiva on the labial side of the canines and incisors. Smokers' melanosis is thus condidered to be caused by tobacco smoking and is expected to be found in other parts of the oral mucosa.