Abstract In the present site-by-site follow-up study, the change in amount of approximal alveolar bone was assessed after 1 year from the baseline examination in 38 and after 2 years in 22 dentate subjects all with insulin-dependent diabetes mellitus. The diabetics, aged 35 lo 56 years at baseline, had a history of a mean duration of 18 years of insulin-dependent diabetes mellitus and were under medical treatment at the outpatient clinic of the III Department of Medicine, University Central Hospital of Helsinki as well as at 2 diabetic clinics of the Helsinki Health Centre. Based upon their Song-term medical records, 26 subjects were after 1 year, and 16 subjects after 2 years from the baseline, identified as having poorly controlled insulin-dependent diabetes (PIDD). At the 1-year examination, 12 subjects were classified as having controlled insulin-dependent diabetes (CIDD) as compared to 6 subjects at the 2-year examination. After 1 and 2 years, from baseline, site-by-site measurements were recorded for plaque index scores, bleeding after probing, loss of attachment, and radiographic loss of alveolar bone. After 1 and 1 years from baseline, the PIDD subjects exhibited higher mean %s of sites with improved bleeding scores (p < 0.01, x3-test) than the CIDD subjects. At the 2-year examination, the mean % of sites with loss of approximal alveolar bone was greater in the PIDD than in the CIDD group (P < 0.05, X3-test). The greatest differences between PIDD and CIDD subjects were found when recordings for only canines were analyzed at the 1 - and 2-year examinations (p<0.05, X2-test). The results of our current 2–year longitudinal site-by-site examinations confirm earlier, results that poorly controlled insulin-dependent diabetes mellitus is strongly related to the amount of alveolar bone loss.