Objective. To estimate the prevalence of physical inactivity among adolescents (aged 14 to 18 years) in the municipality of Maringá, state of Paraná, Brazil and to explore its association with demographic, socioeconomic and behavioral variables and nutritional status indicators. MethOds. Cross-sectional study with a representative sample of 991 high school students (54.5% of girls) from both public and private high schools selected through multi-stage random sampling. Habitual physical activity was assessed using the International Physical Activity Questionnaire (IPAQ) adapted for adolescents, with the previous week taken as reference period. Physical inactivity was defined as <300 min/week of moderate and vigorous physical activity. Independent variables studied were: sex, age, type of school, socioeconomic level, smoking, sedentary behavior (≥4 h/day), nutritional status, and abdominal obesity. Results. The prevalence of physical inactivity among adolescents was 56.9% (girls= 57.9%, boys= 55.7%, p=0.46). Risk factors associated with physical inactivity were lower socioeconomic level, attendance to public schools and obesity. cOnclusiOn. A high prevalence of physical inactivity was found in the population investigated. The development of strategies to increase physical activity among adolescents are urgently needed. It can be achieved through content-based activities that promote a healthy lifestyle.