Objective: to determine the prevalence, severity and extent of chronic periodontitis among 30-60 year old adults residing in Colombo district, Sri Lanka. Basic research design: a cross-sectional study with interviews and oral examinations. Participants: 1400, 30-60 year olds residing in Colombo district. Results: the prevalence of mild, moderate and severe chronic periodontits was 1.4%, 36.1% and 13.5% respectively and the prevalence was significantly associated with sex, age group, ethnicity, level of education, smoking status and selfreported diabetes. The mean probing pocket depth (PPD) was 2.05mm (SE=0.02) and of the sample, 77% and 31% had at least one site with PPD of ≥4 and ≥6mm respectively. The mean clinical attachment loss (CAL) was 2.53mm (SE=0.03) and 99% and 81% of the sample had at least one site with CAL of ≥3mm and ≥5mm respectively. The extent of periodontitis determined according to the mean percentage of sites with ≥4 and ≥6mm of PPD were 8.40 (SE=0.34) and 1.37 (SE=0.11) respectively. Further, the extent of periodontitis according to the mean percentages of sites with ≥3 and ≥5mm of CAL were 39.73 (SE=0.66) and 10.9 (SE=0.43) respectively. Conclusions: the prevalence, severity and extent of chronic periodontits are high among adults in Colombo district. Their periodontal status was poorer than in previously reported studies conducted in the same district. Key words: chronic periodontitis, prevalence, extent, severity, Sri Lanka