Background: Study findings on interpregnancy interval and its effect on low birth weight are contradictory. Some studies report that it is a risk factor for low birth weight while others say it has no association. Still less attention has been given to the way in which changes in family planning related behavior may affect low birth weight. Identifying the interpregnancy interval at which risk of low birth weight is occurred may benefit developing countries to prioritize family planning services.Methods: unmatched case control study design was used in a sample of 453 mothers (88 cases and 365 controls) who gave birth two or more times in Gondar and Bahir Dar teaching-referral hospital, Ethiopia. Cases were mothers who gave birth to low birth weight and controls were mothers who gave normal birth weight. Data was processed and analyzed using EPI Info and SPSS statistical software. A logistic regression was performed to identify the independent effect of interpregnancy interval on low birth weight.Result: The median of interpregnancy interval for cases and controls were 30 and 38 months respectively. The odd of low birth weight was 2.67 (95% CI = 1.36, 5.01) when interpregnancy interval was less than 24 months compared to the interval 24 and above months. Multivariate analysis showed that women who had interpregnancy interval less than 24 months were about 2.7 times more likely in delivering low birth weight infant compared to the interval 24 and above. Likewise women who were age of 20 or less, daily laborer, being moderately or severely food insecure and having pregnancy complication had a significant effect on low birth weight. Conclusion: interpregnancy interval less than 24 months had a significant effect on low birth weight. So mothers at the study area; not be pregnant before 24 months of the birth preceding child. Keywords: birth weight, interpregnancy interval, referral hospital, Ethiopi
