CONTEXT: Both high- and low-dose radiation exposures in women have been associated with low-birth-weight offspring. It is unclear if radiation affects the hypothalamus-pituitary-thyroid axis and thereby indirectly birth weight, or if the radiation directly affects the reproductive organs. OBJECTIVE: To investigate whether antepartum dental radiography is associated with low-birth-weight offspring. DESIGN: A population-based case-control study. PARTICIPANTS AND SETTING: Enrollees of a dental insurance plan with live singleton births in Washington State between January 1993 and December 2000. Cases were 1117 women with low-birth-weight infants (<2500 g), of whom 336 were term low-birth-weight infants (1501-2499 g and gestation > or =37 weeks). Four control pregnancies resulting in normal-birth-weight infants (> or =2500 g) were randomly selected for each case (n = 4468). MAIN OUTCOME MEASURES: Odds of low birth weight and term low birth weight by dental radiographic dose during gestation. RESULTS: An exposure higher than 0.4 milligray (mGy) during gestation occurred in 21 (1.9%) mothers of low-birth-weight infants and, when compared with women who had no known dental radiography, was associated with an adjusted odds ratio (OR) for a low-birth-weight infant of 2.27 (95% confidence interval [CI], 1.11-4.66, P =.03). Exposure higher than 0.4 mGy occurred in 10 (3%) term low-birth-weight pregnancies and was associated with an adjusted OR for a term low-birth-weight infant of 3.61 (95% CI, 1.46-8.92, P =.005). CONCLUSION: Dental radiography during pregnancy is associated with low birth weight, specifically with term low birth weight.