Complications of pregnancy remain a serious threat in Sub-Saharan Africa despite efforts to minimise maternal mortality due to pregnancy complications, and achieve the Millennium Development Goal 5. This is a retrospective study to determine the most common pregnancy complications among adolescents compared to adults treated in a public hospital from 2015 to 2018. The researcher applied a convenience sampling method in selecting the medical records. The instrument used was adapted from previous studies and data were analysed with descriptive and chi-square test for the inferential statistics. A total of 1,265 patients met the eligibility criteria and 540 (42.7%) were adolescents. Low birth weight (n=478, 88.5%) and preterm delivery (n=496, 91.9%) were common among babies born to adolescent mothers. Pregnancy-related complications among adolescent mothers showing the prevalence of anaemia, hypertension, and malaria were 494 (84.9%), 149 (56.2%) and 193 (62.1%) respectively. Gestational diabetes was found to be high among adult mothers (n=98, 74.8%). Among adolescent mothers, the prevalence of eclampsia was 62 (78.5%) and hemorrhage 61 (53.0%). The prevalence of Intrauterine growth restriction (IUGR) was high among adolescent mothers (n=252, 80.5%). Comprehensive strategies are needed to keep girls in schools and to raise awareness and develop campaigns about using contraception properly to reduce the incidence of adolescent pregnancy as well as to minimise the incidence of pregnancy-related complications.