This study investigated the prevalence and factors associated with problematic smartphone use (PSU) in southern Brazil. A total of 411 high school students at a federal institute participated in this research. Smartphone addiction was highlighted as the dependent variable and was assessed using the Smartphone Addiction Scale-Short Version, classifying students of both sexes who scored ≥ 33 on this scale as having PSU. Information on gender, skin color, socioeconomic status, level of physical activity, participation in physical education classes, screen time, and history of binge drinking were organized as independent variables. Poisson regression was used to verify the factors associated with PSU, showing prevalence ratios (PR) with a 95% confidence interval (95%CI). The prevalence of PSU was 34.3% (40.7% female). Adjusted analysis showed significant associations with risk factors (female sex PR = 1.40; 95%CI: 1.06-1.85; screen time PR = 1.48; 95%CI: 1.20-1.82; and history of binge drinking PR = 1.35; 95%CI: 1.02-1.79) and protective factors (higher socioeconomic status PR = 0.88; 95%CI: 0.77-0.99; longer participation in physical education classes PR = 0.73; 95%CI: 0.54-0.99) for PSU. Moreover, students with PSU had worse sleep quality (PR = 1.17; 95%CI: 1.02-1.34), and this effect was more significant in the physically inactive ones (PR = 1.50; 95%CI: 1.13-1.98). Identifying the factors associated with PSU can help raise awareness of the repercussions of this behavior.