Background: Study findings on inter-pregnancy interval and its effect on birth outcome arerncontradictory. Some studies report that it is a risk factor for adverse perinatal outcome whilernothers say it has no association. Still less attention has been given to the way in which changes inrnfamily planning related behavior may affect adverse birth outcome. Identifying therninterpregnancy interval at which risk of adverse birth outcome is occurred may benefitrndeveloping countries to prioritize family planning services.rnObjective: To asses effect of short interpregnancy interval on adverse birth outcome in Gondarrnand Bahir Dar teaching- referral hospitals, Ethiopia.rnMethods: Unmatched case control study design was used in a sample of 548 mothers who gavernbirth two or more times in Gondar and Bahir Dar teaching-referral hospital, Ethiopia. Cases werernmothers who gave birth to LBW or preterm or stillbirth and controls were mothers who gavernnormal birth weight or term or live birth. Data were processed and analyzed using EPI Info andrnSPSS statistical software. A logistic regression was performed to identify the independent effectrnof interpregnancy interval on adverse birth out come.rnResult: The median of interpregnancy interval for cases and controls were 32 and 38 months,rnrespectively. The odd of adverse birth outcome was 2.36 (95% CI = 1.36, 4.08) for womenrnhaving interpregnancy interval less than 24 months compared with the interval 24 and above.rnThe odd of low birth weight was 2.67 (95% CI = 1.36, 5.01) when interpregnancy interval wasrnless than 24 months compared to the interval 24 and above months. The odd of preterm birth wasrn2.92 (95% CI = 1.39, 6.12) for women having interpregnancy interval less than 24 months.rnMultivariate analysis showed that women who had interpregnancy interval less than 24 months rnwere about 2.5 times more likely in resulting stillbirth compared to the interval 24 and above. rnConclusion: Interpregnancy interval less than 24 months had a significant effect on adverse birthrnoutcome. So birth spacing education, counseling, and services should be given to women not tornbe pregnant before 24 months; as adverse birth outcome reduction strategies.