Back ground The adverse birth outcomes can lead to higher rates of illness and infection for newborns, as well as long-term neurological and health problems. Hence, this study aims to identify determinants of adverse birth outcomes among mothers who gave birth in hospitals in the west shewa zone, Ethiopia. Methods Unmatched case-control study was conducted among 591 mothers (146 cases and 445 controls) who gave birth at hospitals found in the west Shewa zone from March 2020 and July 2020. All cases during the data collection period and every 3rd control after cases were selected as a study population. The data were collected from the mothers, measurements from neonates. The questionnaire template was coded by using open source software for Computer-Assisted Personal Interviewing using census and survey processing system (CS-Pro) version 7.1. The collected data were exported to SPSS version 23 for analysis. Finally, presented and interpreted at P-value < 0.05 were considered as statistically significant in multivariable logistic regression.Result: on multivariable analysis; urban residence (AOR=0.56, 95%, CI=0.36-0.88), lack of family support during child bearing (AOR=5.07, 95% ,CI: 3.01-8.54), pregnancy type(3.994 (AOR=3.4, 95% ,CI: 2.04-7.83,), short inter pregnancy interval (AOR=1.6, 95% CI: 1.99-2.48), not provided all initial newborn care (AOR=2.19, 95% CI: 1.39-3.41), less than four antenatal care visits (AOR=1.6, 95% CI: 1.02-2.61) and having current obstetric complication (AOR=2.7, 95% CI: 1.55-4.84) were significantly associated with adverse birth outcomes. Conclusions: Residence, lack of family support during child bearing, Pregnancy type, short inter pregnancy interval, not provided first initial newborn care, having current obstetric complications, and Number of ANC visits were identified as determinants of adverse birth outcome. Therefore, improving family support, inter-pregnancy interval through family planning counselling and provision, providing all initial newborn cares, and having the recommended ANC follow-up was recommended.