<p>Mann-Whitney U Test by gender.</p>

Adolescent depression is a growing public health concern, particularly in low- and middle-income countries where mental health resources are limited. This study aimed to assess the prevalence of depressive symptoms among secondary school adolescents in the Dodoma and Pwani Regions of Tanzania and to explore associations with key demographic factors. A cross-sectional survey was conducted among 1009 secondary school adolescents in the Dodoma and Pwani regions of Tanzania. The Swahili version of the Patient Health Questionnaire-9 (PHQ-9) was used to assess depressive symptoms. Descriptive statistics were used to determine prevalence, while associations between depression scores and demographic variables were analysed using Chi-square, one-way ANOVA, Mann-Whitney U, and Kruskal-Wallis H tests, with the magnitude of association reported as Cramér’s V for the Chi-square test. Overall, 62% of adolescents exhibited depressive symptoms ranging from mild to severe, with 37% mild, 17% moderate, 6% moderately severe, and 2% severe. Depressive symptoms were significantly associated with age, region, gender, and parental living arrangement (p < 0.05). A higher prevalence was observed among females, adolescents aged 14–17 years, residents of Dodoma, and those living with a single parent. Effect size analysis indicated a strong association with region and a moderate association with parental living arrangement, while gender and age showed smaller but meaningful associations. Depression among Tanzanian adolescents in Dodoma and Pwani is prevalent and significantly associated with key demographic and psychosocial factors.