Dissertation (MMED Obstetrics and Gynaecology)Background: Pregnancy during teenage is the high risk which is associated with high incidence of complications to the mother and fetus. Worldwide the incidence of teenage pregnancies is reported to range from 8-25% in developing countries due to child marriages. Poor obstetric outcomes have been reported by previous studies. These depend largely on the age of the teenagers and the quality of care she receives. Objectives: The study aimed to assess the magnitude and immediate obstetric outcomes in teenage primegravida arriving in active first stage of labour at Iringa regional referral hospital. Methods: The study was a hospital based cross-sectional study with prospective follow-up with sample size of 210 teenage primegravida (11-19 years) were involved. Data were collected using a pretested checklist to obtained desired information. Data analysis was done by using SPSS version 23. Results: During the study period a total number of 1921 deliveries took place at the hospital during the study period. Out of 1921, 210 (10.9%) were teenage primegravida. 137 (65.2%) delivered by spontaneous vaginal delivery. Maternal complications observed include perineal tear (32.4%), PPH (4.8%) and cervical tear (3.3%). The fetal complication observed include low APGAR score (<7) (9.5%), low birth weight (6.7%), 15.7% of newborns needed admission into NICU and (4.3%) neonatal death. No maternal death among teenagers during the study period. Conclusion: High prevalence and adverse outcomes observed in teenage primegravida in this study may be due low education level and unmarried status. This calls for committed and sustained efforts to address the problem and education on prevention of teenage pregnancy to reduce complications of teenage pregnancy and associated complications