Teenage pregnancy remains a significant public health concern globally, especially in low- and middle-income countries like Tanzania. It contributes to increased maternal and fetal morbidity and mortality, including complications such as anemia, hypertensive disorders, obstetric hemorrhage, low birth weight, and preterm delivery. Despite various interventions, teenage pregnancy rates remain high. This study aimed to assess obstetric outcomes and associated factors of teenage pregnancy in Mwanza region, Tanzania. A hospital-based cross-sectional study was conducted from April to June 2019 in four hospitals: Misungwi District Hospital, Sengerema District Designated Hospital, Bugando Medical Center, and Sekou Toure Regional Referral Hospital. A total of 357 teenage mothers who met inclusion criteria participated. Data were collected using structured questionnaires and checklists, then analyzed using STATA version 13. The mean age of participants was 17±1.3 years, with 72% from rural areas and 85.7% having no education or only primary education. Most were primiparous (90.2%) and had booked antenatal care (98.9%), though attendance and service utilization were inadequate. Vaginal delivery was common (79.2%). Adverse maternal outcomes included perineal tears (28.4%), anemia (59.7%), and hypertensive disorders (11.8%). Fetal outcomes showed 75% healthy live births, with occurrences of low birth weight (12.9%), small for gestational age (37.2%), and prematurity (14.8%). Hypertensive disorders were independently associated with poor fetal outcomes. The study concludes that teenage pregnancy is high-risk, often leading to adverse maternal and neonatal outcomes, highlighting the need for targeted interventions.