Rapid digital penetration across India has transformed adolescents’ behavioural landscape, particularly in semi-urban and rural districts such as Dakshin Dinajpur in West Bengal. While smartphones enhance access to information and social connectivity, concerns regarding addictive use and its psychological consequences are escalating. Using a descriptive cross-sectional survey design, this study investigated the prevalence, demographic variations, and mental-health correlates of smartphone addiction among 400 adolescents aged 13–18 years. Data were collected using the SAS-SV and DASS-21. Findings revealed an addiction prevalence of 38.5%. A significant gender difference was observed, χ² (1, 400) = 4.62, p = .032, with girls showing greater vulnerability. Addicted adolescents reported significantly higher depression, t (398) = 6.21, anxiety, t (398) = 5.74, and stress, t (398) = 6.48, all p < .001. Pearson correlations indicated strong positive associations between addiction and psychological distress (e.g., stress: r = .44, p < .001). Logistic regression identified daily smartphone use (OR = 1.54), gender (OR = 1.37), and depressive symptoms (OR = 1.22) as significant predictors. The findings highlight the need for district-level digital-literacy initiatives, routine mental-health screening, and school-based intervention strategies to safeguard adolescent well-being in rapidly digitizing communities.