Periodontal health in 37 patients with a 47,XXY chromosome complement (Klinefelter Syndrome) and in 12 brothers of patients was studied. Mean age-adjusted Gingival, Gingival Bleeding and Calculus Indices were statistically significantly higher in 47,XXY men than in the controls. The mean percentage of tooth surfaces with pathologically deepened probing depths for all 47,XXY men was 8.5%, for the subgroup of 47,XXY men with brothers it was 7.1%, and for the brothers it was 7.5%. Tooth mobility was found in two 47,XXY men and in one control. The results indicate that gingival inflammation was increased in the 47,XXY men than in the controls.