There is no consensus about the influence of periodontal disease on preterm low birthweight. The objective was to investigate the relationship between periodontal disease and preterm low birthweight. A case-control study with 542 post partum women aged over 30 yrs was conducted. Three groups of cases were compared with non-preterm and non-low-birthweight control individuals (n = 393): low birthweight (n = 96), preterm (n = 110), and preterm and low birthweight (n = 63). Periodontal clinical parameters and covariates were recorded. Periodontal disease levels were higher in control individuals than in cases. The extent of periodontal disease did not increase risk of preterm low birthweight according to 15 measures of periodontal disease. Mean periodontal pocket depth and frequency of periodontal sites with clinical attachment level > or = 3 mm in preterm low birthweight cases were lower than in control individuals. Periodontal disease was not more severe in women with preterm low birthweight babies.