The aim of this study was to assess the effect of overweight and obesity on periodontal attachment loss (PAL) progression in an urban population from south Brazil. In 2001, a population-based oral health survey entitled "Epidemiology of periodontal diseases: the Porto Alegre Study" was conducted by drawing a probabilistic sample of 1586 individuals. After 5years, 755 (participation rate: 47.6%) individuals were re-examined. For this analysis, self-reported diabetics, underweight individuals, and individuals with <6 teeth were excluded. Poisson regressions were used to calculate relative risks (RR) and 95% confidence intervals (CI) adjusted for sex, age, skin colour, education, socio-economic status, smoking and dental care. Five hundred and eighty-two individuals (333 males/249 females, 36.02±14.97years) were included. Overall, obese individuals had significantly higher risk of experiencing PAL progression than individuals with normal weight after adjusting for important co-factors (RR=1.36, 95% CI=1.04-1.78). In a stratified analysis, no statistically significant associations were observed between PAL progression and obesity for males (RR=1.13, 95% CI=0.75-1.69), whereas obese females were at statistically significant higher risk than normal weight females (RR=1.64, 95% CI=1.11-2.43). Obesity appears to be a risk factor for PAL progression for females but not males in this developing country population.