OBJECTIVE: In 2010, American youth aged 8 to 18 spent an average of 7.5 hours daily using entertainment media, an increase of more than an hour compared with 2005. Increase in media use is associated with multiple negative outcomes, including decreased sleep time and increased tiredness, but little research has examined whether media use is associated with poorer sleep efficiency when the individual is actually asleep. METHODS: This study assessed relations between adolescent media use and sleep efficiency. Fifty-five adolescents (mean age = 14.89 years; SD = 0.62; 53% African-American and 47% white) completed self-report measures concerning their media use. Sleep quality was measured by actigraphy for 1 week, and both sleep offset and sleep efficiency were extracted from actigraphy data. RESULTS: Sleep efficiency was negatively correlated to daily time spent text messaging (r(52) = -0.29; p < .05), media use after bed (r(52) = -0.32; p < .05), and number of nighttime awakenings by mobile phones (r(52) = -0.33; p < .05). Decreased sleep efficiency was related to sleeping later in the morning, presumably to make up for lost sleep at night (r(52) = -0.33; p < .05). In a regression model, media use accounted for 30% of the variance in sleep efficiency (adjusted R = 0.30; F(6,44) = 3.74; p < .01). CONCLUSION: Media use after bed, awakenings by a mobile phone at night, and sleep offset associated with adolescents' sleep efficiency. Results support the incorporation of media use habits into adolescent sleep health education and sleep dysfunction interventions. Parental education about the effects of media use on sleep could also mitigate negative effects.