A Retrospective Analysis of Adolescent Pregnancy and Child Mortality Cases in Kota Kinabalu, Sabah Introduction Under-five mortality remains a critical public health challenge, particularly among vulnerable and underserved populations. This study aimed to identify distinct socio-clinical profiles associated with under-five deaths in Kota Kinabalu from 2020 to 2024 and to compare risk patterns between adolescent and adult mothers using cluster analysis. Methods A retrospective analysis of district health records was conducted. A total of 818 under-five mortality cases were included, of which 55 involved adolescent mothers (10–19 years). K-means clustering was applied to maternal-socioeconomic and clinical variables to identify distinct profiles. The optimal number of clusters was determined using silhouette scores and stability testing. Associations between cluster membership and maternal-child health variables were evaluated using chi-square tests. Results Three clusters emerged. Cluster 2 represented the most vulnerable group, predominantly comprising non-citizen adolescent mothers with no formal education, household incomes below RM 1,000, and inadequate antenatal care. This cluster exhibited the highest rates of preterm births and preventable under-five deaths. Significant associations were identified between cluster membership and maternal age, citizenship status, education level, antenatal care, and birth outcomes. Under the death category, 61.7% of child deaths were classified as preventable, highlighting areas for intervention, while 38.3% were deemed not preventable. Conclusions Intersecting social disadvantages such as young maternal age, non-citizenship, low education, and poverty amplify risks for both mothers and children. Addressing these broader determinants through culturally sensitive, accessible maternal health services and targeted adolescent outreach is essential. Integrating cluster analysis into surveillance can enable early identification of high-risk groups and support equity-focused interventions to reduce preventable child mortality.