Abstract: Introduction: Adolescents exhibit present reduced hours of sleep and greater prevalence of daytime sleepiness as a result of the interaction of maturational, behavioral, and environmental factors. Until the present moment, one does not dispose of the prevalence of daytime sleepiness or the association of innumerous factors to low sleep duration in population studies involving Brazilian adolescents. Objective: To investigate the prevalence and factors associated with short sleep duration, daytime sleepiness (DS) and classroom sleepiness (CS) in adolescents in high school in the municipality of Santa Maria, RS, Brazil Method: The sample of this study was formed by 1126 high school students (55.1% female), aged from 13 to 21 years, with an average age of 16.24(1.39), from public schools in the municipality of Santa Maria. The dependent variables analyzed were sleep duration, DS and CS. The associated investigated encompass biological, environmental and behavioral aspects. Adjusted bivariate and multivariate analyses were carried out. Results: 54.8% of the adolescents present eight or less hours of sleep during school days. The prevalence of DS and CS were 25% and 27.1%, respectively. Male students presented shorter sleep duration (p=0.002), but female students presented greater prevalence of DS (p=0.002) and CS (p=0.02). Longer commuting time to school were associated with shorter sleep duration (p=0.046). In the final adjusted models, short duration of sleep was associated to the periods of school study (p=0.016) and to changes to morning class schedules (p<0.001). The main factors associated to DS were CS (p<0.001), naps (p=0.001) and minor psychic disorders (p=0.046). However, CS associated change to a morning class schedule (p=0.047), DS (p=0.021) and the presence of minor psychic disorders (p=0.048). Beyond that, the factors of residential neighborhood, sleep quality, probably allergic rhinitis, stress, fat and alcohol consumption and taking shower before school were associated to CS in the adjusted analyses. Conclusions: More than half of the adolescents investigated were classified with short sleep duration, which justify the need for interventions in order to increase sleep duration. Minor psychic disorders and changing to a morning class schedule were variables especially associated to greater indicators of sleepiness and short sleep duration. Taking shower before school may be a possible recommendation aiming the reduction of sleepiness in the classroom. The recommendation of active commuting to school must be done carefully to avoid an increase of the reduction of sleep duration in adolescents.