Psychological disturbances may lead patients to neglect oral hygiene. This study investigated whether a number of psychosocial factors (depression, state and trait anxiety, total and average perceived stress, and loneliness) could predict dental plaque levels in patients with adult onset rapidly progressive periodontitis (RPP) and routine chronic adult periodontitis (RCAP), before periodontal treatment. It was also examined whether RPP and RCAP patients differed on plaque and smoking. Plaque was scored in a sample of 6 teeth in each of 80 subjects, 40 with RPP, 40 with RCAP, before psychosocial questionnaire completion. Multiple regression was performed between plaque as the dependent and psychosocial factors, gender, education, form of periodontitis and smoking as independent variables. Only gender contributed significantly to prediction of plaque, t=-2.70, p=0.01, partial regression coefficient -0.37, 95% CI: -0.64 to -0.10, indicating that plaque was on average 0.37 lower for females than males, after adjusting for the other predictor variables. It was confirmed that RPP and RCAP patients did not differ significantly on plaque, univariate t-test(69.99)= 0.65, p=0.13. However, RPP patients smoked significantly more than RCAP patients t(69.72)=2.36, p=0.02. There was also a marginally significant correlation between depression and smoking, r=0.16, p=0.07. One possible reason advanced for the lack of an association between psychosocial factors and plaque, and the absence of a difference in plaque between RPP and RCAP patients is the fact that the patients involved in the present study were seen as secondary referrals. The gender difference in plaque levels and the greater incidence of smoking in RPP patients may be of significance in planning interventions with patients with periodontitis.