OBJECTIVES We compared rates of risky driving among novice adolescent and adult drivers over the first 18 months of adolescents' licensure. METHODS Data-recording systems installed in participants' vehicles provided information on driving performance of 42 newly licensed adolescent drivers and their parents. We analyzed crashes and near crashes and elevated g-force event rates by Poisson regression with random effects. RESULTS During the study period, adolescents were involved in 279 crashes or near crashes (1 involving injury); parents had 34 such accidents. The incidence rate ratio (IRR) comparing adolescent and parent crash and near-crash rates was 3.91. Among adolescent drivers, elevated rates of g-force events correlated with crashes and near crashes (r = 0.60; P < .001). The IRR comparing incident rates of risky driving among adolescents and parents was 5.08. Adolescents' rates of crashes and near crashes declined with time (with a significant uptick in the last quarter), but elevated g-force event rates did not decline. CONCLUSIONS Elevated g-force events among adolescents may have contributed to crash and near-crash rates that remained much higher than adult levels after 18 months of driving.