Objective: To examine associations between in utero marijuana exposure and birth outcomes. Study design: In two separate cohorts (Appalachian, Rocky Mountain), data were collected from medical records. Marijuana exposure was positive based on urine drug screening at delivery, with nonexposed controls matched on multiple factors including other substance exposure. Result: Marijuana-exposed newborns (n = 531) had significantly worse birth outcomes than controls (n = 531), weighing 218 g less, 82%, 79%, and 43% more likely to be low birth weight, preterm, or admitted to the NICU, respectively, and significantly lower Apgar scores. Conclusion: Marijuana exposure in utero predicted newborn factors linked to longer-term health and development issues. Effects were not attributable to other comorbidities in this study due to rigorous matching and biochemical verification of marijuana and other drug use. Findings add to growing evidence linking marijuana exposure to adverse birth and longer-term outcomes. Women should be encouraged to avoid marijuana use during pregnancy.