<bold>Purpose.</bold> The aim of this study was to investigate the associations between health-related physical fitness and sociodemographic factors in students from a capital city of a Brazilian state. <bold>Methods.</bold> A cross-sectional study was conducted on 605 students aged 15 to 19 years. Sociodemographic data were collected, including gender, age, education level and family income, and correlated to physical fitness levels. <bold>Results.</bold> The percentages of students with unhealthy body composition, unhealthy skeletal muscle fitness and aerobic fitness levels were 23.8%, 34.4% and 30.5%, respectively. There was a trend for fewer male adolescents (OR: 0.65; IC95%: 0.42-0.98) to have unhealthy body composition. Students from lower socioeconomic families were less likely to have musculoskeletal unfitness (OR = 0.60; IC95%: 0.41-0.89). In relation to aerobic fitness, male students (OR = 3.86; IC95%: 2.67-5.58) and those aged 17-19 years (RO = 1.49; IC95%: 1.02-2.177) were more likely to be unfit. <bold>Conclusions.</bold> It is important to encourage young people to take part in sports and physical activities at moderate to vigorous intensities in order to improve their body composition, aerobic capacity and physical fitness.