An initial screening investigation of 1681 Swedish urban adults aged 31-40 years with untreated periodontitis showed that 17.2% (289) had at least one site with probing depth > or = 5 mm. The 289 subjects were offered a complete clinical examination and treatment. 144 subjects, 85 men and 59 women, agreed to participate and 145 were non-responding subjects and used as a drop out sample. The results from the screening data showed that the attendants had poorer oral hygiene status and more severe periodontitis than the drop out subjects. The present report describes clinical data of this representative sample with adult periodontitis. Clinical indices were recorded and bone height (BH%) for all teeth was measured with a computer digitizing system. In the 144 attendants, Plaque Index was > 1 in 56.2%, Calculus Index was > 1 in 57.0%, Gingival Index was > 1 in 97.2% and bleeding on probing was found in 89.1% of the sites. 11.1% of the subjects had 1-3 teeth with probing depth > or = 5 mm, 59.0% 4-10 teeth, 25.7% 11-20 teeth and 4.2% > 20 teeth. 47.9% of the subjects had mean BH% less than 80. 45.1% of the subjects had at least one site with an intrabony defect, of which 20% had 3-4 sites and 27.7% > or = 5 sites. It is concluded that advanced generalized periodontitis exists in a limited number of 31-40 year-olds in Sweden. Specific risk factors may be involved in the pathogenesis of the disease.