Introduction: It is known for a long time that tooth and gingival infections may have long distance organic repercussions. Recently, it has been suggested that periodontal disease in pregnancy could be a cause of low weight at birth. Objective: To evaluate the influence of periodontal disease in pregnancy on the birth weight of the newborn infants. Patients and Methods: Mothers who gave birth to low-birth-weight infants were randomly selected (Group 1 - G1; n=13). Immediately after inclusion of each mother in group 1, the mother of the next term newborn with birth weight of > 2,500 g (Group 2 - G2; n=13) was included as control. Mothers were examined by a periodontist who was not informed of the group the child belonged to. A probe was used to measure attachment loss of the alveolar bone. The extension index (EI) and severity index (SI) of the periodontal disease were determined. Results: Both groups of mothers were similar in terms of maternal age, parity, color of skin, height, nutrition, smoking, drinking, socioeconomic status, prenatal examinations, premature rupture of membranes, chorioamnionitis, bacteriuria, placenta previa , abruptio placentae, previous hypertensive disease, preeclampsia, and heart disease. The characteristics of the newborns were: birth weight - G1 = 1,804 ± 675 g x G2 = 3,030 ± 516 g; gestational age - G1 = 33 ± 5 weeks x G2 = 39 ± 2 weeks; length of stay in the neonatal intensive care unit (NICU) - G1 = 128 days x G2 = 0 days. Average EI: G1 = 89.788 ± 18.355 x G2 = 72.420 ± 20.717; p=0.033. Average SI: G1 = 1.377 ± 0.626 x G2 = 0.754 ± 0.413 (OR=18.3; CI95%: 2.5-133.3; p = 0.006). After adjustment for risk factors for low birth weight, such as smoking, maternal height, bacteriuria, and previous hypertension, the odds ratio for SI dropped to 7.2 (CI95% = 0.4-125.4; P = 0.176). Conclusion: The multivariate analysis indicated a marked association between periodontal disease measured by SI score and low birth weight. Our data suggested that periodontal disease during pregnancy may be a risk factor for low weight at birth.