Introduction: Despite the numerous adolescent pregnancy prevention interventions implemented, Uganda has persistently had a high prevalence of adolescent pregnancy (25%) for the last ten years. This study sought to identify the predictors of adolescent pregnancy among adolescent girls aged 15-19 years in school. Methods: A cross sectional study design was used. Data was collected from 988 girls aged 15-19 years attending secondary school from twenty secondary schools in August 2019 using a structured questionnaire. Descriptive statistics and inferential analysis was done using SPSS. Results: The factors that that were associated with adolescent pregnancy at bivariate analysis were religion, school section (day scholar or boarding) category, ever been pregnant, ever had an abortion, sexual behavior and ever used family planning. At multivariate analysis, school section (day scholar or boarding) category and sexual behavior of the school girls were statistically significant. A higher proportion of the school girls in the boarding section got pregnant (3.6%) compared to girls who were day scholars (1%).