Introduction: Teen age pregnancy has poor maternal and neonatal outcome but the proportion and associate factor were not well known. Therefore, the purpose of this investigation was to assess the proportion and associated factors of teen age pregnancy among pregnant women visiting the health institution in Bibugn District, north west Ethiopia. Method: Institutional based prospective cross-sectional study would be conducted from April 1,2021 to June 30,2021 from all pregnant women visiting health institution in Bibugn district, north west Ethiopia. Three hundred forty six study unit would select by systematic random sampling every other cause (K=2) during time of institutional visit among all pregnant women in antenatal, delivery and other service area. Data would collect by self administered questioner and face to face interview of data collector. The data checked its completeness and validity daily by supervisor and weekly by principal investigator. The collected data would enter to Epidata 3.1 statistical soft ware and transfers to SPSS version 25 for analysis. Data analysis would done by using bi-variable analysis and variable with p- value of less than 0.25 are select for multivariable analysis using binary logistic regression. Variable at 95% confidence interval with p-value of less than 0.05 are significantly associated to teen age pregnancy were selected and expressed interims of odds ratio. Finally the finding of result expressed in the form of percent, mean and frequency by using table. Result finding compare with different variable of the study each other and previous study finding mentioned in the literature. Result: The proportion of teen age pregnancy among pregnant women visiting health institution in Bibugn district for antenatal follow up during study period was 19.5% (65). The Most common case of teen age pregnancy identified are sexual intercourse before the age of 18 year due to early marriage, or premarital sexual intercourse like Desire to sexual engagement (6.3%), rape (3.6%), peer pressure(2.1) and other (0.9%). Live in rural residence AOR 5.544 ( CI =1.993-15.428), from occupation of participant binge a student AOR 4.898 (CI =1.272-18.865), absence of open discussion on reproductive health in the family AOR 2.479 ( CI=1.106-5.558) and non contraception use AOR 4.707 (CI = 1.913-11.582) were significantly associated to teenage pregnancy in the study area. Discussion and recommendation: Varity of factors affect proportion of teen age pregnancy in the district like residence, head of house hold being father in the family, absence of open discussion on reproductive and sexual health in the family and non contraception usage. Encouraging sexual and reproductive health communication activity, empowering women on decision making activity and scale up awareness of the community on free discussion in the house hold related to sexual and reproductive health.