BACKGROUND: College-age individuals have the highest incidence of pedestrian injuries of any age cohort. One factor that might contribute to elevated pedestrian injuries among this age group is injuries incurred while crossing streets distracted by mobile devices. OBJECTIVES: Examine whether young adult pedestrian safety is compromised while crossing a virtual pedestrian street while distracted using the Internet on a mobile "smartphone." METHOD: A within-subjects design was implemented with 92 young adults. Participants crossed a virtual pedestrian street 20 times, half the time while undistracted and half while completing an email-driven "scavenger hunt" to answer mundane questions using mobile Internet on their cell phones. Six measures of pedestrian behavior were assessed during crossings. Participants also reported typical patterns of street crossing and mobile Internet use. RESULTS: Participants reported using mobile Internet with great frequency in daily life, including while walking across streets. In the virtual street environment, pedestrian behavior was greatly altered and generally more risky when participants were distracted by Internet use. While distracted, participants waited longer to cross the street (F=42.37), missed more safe opportunities to cross (F=42.63), took longer to initiate crossing when a safe gap was available (F=53.03), looked left and right less often (F=124.68), spent more time looking away from the road (F=1959.78), and were more likely to be hit or almost hit by an oncoming vehicle (F=29.54; all ps<0.01). Results were retained after controlling for randomized order; participant gender, age, and ethnicity; and both pedestrian habits and mobile Internet experience. CONCLUSION: Pedestrian behavior was influenced, and generally considerably riskier, when participants were simultaneously using mobile Internet and crossing the street than when crossing the street with no distraction. This finding reinforces the need for increased awareness concerning the risks of distracted pedestrian behavior.