OBJECTIVES: On the basis of information from studies of older adults, smoking is considered to be an important risk factor for periodontal disease. Examining periodontal loss of attachment among younger adults means a lower contribution from cumulative exposure to other environmental risk factors. The aim of this study was to examine the role of chronic exposure to cigarette smoking as a risk factor for greater prevalence and extent of periodontal loss of attachment among 26-year-old participants in a longstanding prospective cohort study. METHODS: Loss of attachment (LOA) was measured at three sites per tooth in two randomly selected contralateral quadrants (one upper, one lower). Cigarette smoking history was obtained at ages 15, 18, 21 and 26, and used to categorise participants as "never-smokers", "ever-smokers", "long-term smokers" or "very longterm smokers". RESULTS: Periodontal data were available for 914 Study members, among whom the prevalence of LOA of 4+mm was 19.4%. Among those who smoked at ages 15, 18, 21 and 26, it was 33.6%, and, after controlling for sex, selfcare and dental visiting, they were nearly three times as likely to have one or more sites with 4+mm LOCONCLUSIONS: Chronic exposure to smoking is a strong predictor of periodontal disease prevalence in young adults.