Exposure to a number of environmental, behavioral and sociodemographic variables has been associated with increased prevalence and severity of adult periodontitis. However, it is not possible easily to identify the individuals most susceptible to this chronic disease. A case control study was conducted among a population of adults to determine what factors were associated with increased prevalence of moderate to advanced periodontitis. Clinical and radiographic data were obtained from dental charts and structured interviews were conducted by telephone to collect sociodemographic and behavioral data. Statistical modeling was completed for the total study population (35-87-year-olds) and for two age-stratified subpopulations. Significant crude disease associations were observed between periodontitis and numerous explanatory variables. However, after adjustment for age and gender, few variables remained significant. Age stratification indicated that young adults (35-54 years) were affected differently from older adults (> or =55 years) by exposures to certain variables. Young moderate smokers had a 3.15 times increased risk of periodontitis and young heavy smokers had a 7.33 times increased risk compared to never-smokers. Older single adults had a 3.07 times increased risk compared to those with partners.