Accelerometers are widely used to measure physical activity and sedentary behaviour amongst youth, and research participants have to wear the accelerometer for enough time to provide valid estimates of their habitual behaviour. This study aimed to identify correlates of accelerometer wear time in a sample (n = 142) of Brazilian adolescents of the 7th to the 9th grade. Students of two middle schools of Florianopolis were invited to participate. The participants answered a questionnaire, wore an accelerometer on the right hip for 10-12 days, and had their height and weight measured. The association of gender, age, socioeconomic position, mother education, conicity index, and self-reported physical activity with accelerometer wear time (minutes), number of days with ≥ 10h of valid accelerometer data, and compliance with validation criteria (≥ 4 days with ≥ 10h of wear time, including a weekend day) were tested. Accelerometer wear time in minutes was lower in boys than girls (-1014.14, 95%CI: -1822.91; -205.37). Boys also had less valid days compared to girls (Incidence Risk Ratio = 0.70; 95%CI: 0.52; 0.94) and were less likely to comply with validation criteria (Odds Ratio = 0.29; 95%CI: 0.12; 0.68). Higher mother education was associated with increased odds of meeting validation criteria. Factors associated with compliance with accelerometer protocol were sex and mother education. Thus, analyzes should consider the difference in representation of such groups.