The calculus (OHI-S) index according to Greene and Vermillion and the periodontal disease index of Kötzschke were determined in 209 male diabetics. The calculus index (CI) was significantly lower in diabetics with healthy gingivae (CI=0.40) than in diabetics with pathological periodontal findings (CI=1.40). Diabetics with advanced periodontal diseases (gingival recession, periodontitis and pockets), such as parodontopathia inflammata profunda, showed the highest CI value (1.88) which also differed significantly from the CI values for diabetics with healthy gingivae or with parodontopathia inflammata superficialis. 91% of our diabetics with pathological findings showed also concretions of calculus, subgingival concretions being detectable in 47.4% of these patients. It is concluded from results obtained that calculus formation is surely a sequela but not the only cause of periodontal diseases.