OBJECTIVE To examine whether there are associations between pregnancy intention (intended, unwanted, mistimed, or ambivalent) and negative birth and maternal outcomes: low birth weight (less than 2,500 g), preterm delivery (fewer than 37 weeks), small for gestational age, premature labor, hypertension, and other maternal outcomes. METHODS We analyzed data from the population-based Pregnancy Risk Assessment Monitoring System, including 87,087 women who gave birth between 1996 and 1999 in 18 states. Information on pregnancy outcomes was derived from birth certificate data and a self-administered questionnaire completed postpartum. We employed SUDAAN (RTI International, Research Triangle Park, NC) for univariable and logistical regression analyses. RESULTS In analyses controlling for demographic and behavioral factors, women with unwanted pregnancies had an increased likelihood of preterm delivery (adjusted odds ratio [OR] 1.16, 95% confidence interval [CI] 1.01-1.33) and premature rupture of membranes (adjusted OR 1.37, 95% CI 1.01-1.85) compared with women with intended pregnancies. Women who were ambivalent toward their pregnancies had increased odds of delivering a low birth weight infant (adjusted OR 1.15, 95% CI 1.02-1.29); in contrast, women with mistimed pregnancies had a lower likelihood (adjusted OR 0.92, 95% CI 0.86-0.97). CONCLUSIONS Pregnancy intention, specifically unwanted and ambivalent, may be an indicator of increased risk for some poor birth and maternal outcomes and should be considered in interventions aimed at improving the health of the mother and child. METHODS III.