The overall periodontal states of 81 women with 45,X chromosome complement (Turner's Syndrome) and a sister of 31 of these women were studied. The ages of the subjects ranged from 13 to 35 years. Mean Gingival Index and Calculus Index values were lower in all 45,X women studied and in a subgroup of 45,X women whose sisters formed the control group than in the controls. When the effect of age was taken into account differences were similar. Pathologically deep probing depths of 4 mm or over were found in 9 (11.1%) of all 45,X women, in 3 (9.7%) of the subgroup of 45,X women whose sisters formed the control group and in 7 (22.6%) of the controls. The results indicate that periodontal health was better in the 45,X females than in the controls.