Objective-The purpose of the study was to examine the relationship between self-reported sleep quality and sleep hygiene in Italian and American adolescents and to assess whether sleephygiene practices mediate the relationship between culture and sleep quality.Methods-Two nonprobability samples were collected from public schools in Rome, Italy, and Hattiesburg, Mississippi. Students completed the following self-report measures: Adolescent Sleep-Wake Scale, Adolescent Sleep Hygiene Scale, Pubertal Developmental Scale, and Morningness/Eveningness Scale.Results-The final sample included 776 Italian and 572 American adolescents 12 to 17 years old. Italian adolescents reported much better sleep hygiene and substantially better sleep quality than American adolescents. A moderate-to-strong linear relationship was found between sleep hygiene and sleep quality in both samples. Separate hierarchical multiple regression analyses were performed on both samples. Demographic and individual characteristics explained a significant proportion of the variance in sleep quality (Italians: 18%; Americans: 25%), and the addition of sleep-hygiene domains explained significantly more variance in sleep quality (Italians: 17%; Americans: 16%). A final hierarchical multiple regression analysis with both samples combined showed that culture (Italy versus United States) only explained 0.8% of the variance in sleep quality after controlling for sleep hygiene and all other variables.Conclusions-Cross-cultural differences in sleep quality, for the most part, were due to differences in sleep-hygiene practices. Sleep hygiene is an important predictor of sleep quality in Italian and American adolescents, thus supporting the implementation and evaluation of educational programs on good sleep-hygiene practices. Adolescence is a period characterized by important changes in cognitive, behavioral, social, and emotional functioning attributable to biological development (ie, puberty) and to new roles and demands in the familial and social milieu (eg, decreased parental involvement, increased academic requirements). There also are dramatic changes in sleep/wake patterns during adolescence, including a decrease in sleep duration, 1-3 a delay in the timing of sleep, 4,5 and an increasingly large discrepancy between weekday and weekend sleep patterns. 6-9 Sleep quality is reduced as well. 10 Community-and school-based studies conducted in Europe, Asia, and the United States suggest that between 6% and 37% of adolescents report difficulties on ≥1 of the following behavioral dimensions of sleep quality: going to bed, 11,12 falling asleep, 3,13-17 maintaining undisturbed sleep, 10,16-18 reinitiating sleep after nocturnal awakenings, 3,16,17 and returning to wakefulness in the morning. 7,9,15,17 Furthermore, up to 16% of adolescents are considered to have clinically significant insomnia. 16,19,20 There is ample evidence that inadequate sleep quantity and quality are linked to significant problems in several aspects of teenagers' lives. 5,8 Sleepiness ...