Background: HIV-positive pregnant women are at an increased risk of adverse pregnancy outcomes. However, data on birth outcome among HIV-infected women are limited in Ethiopia. This study was conducted to identify the adverse birth outcomes and associated factors of low birth weight (LBW) and preterm delivery (PD) among HIV-infected women. Methods: A hospital based retrospective cohort study was conducted. All deliveries from HIV-infected women from September 1, 2009 to April 30, 2012 were included in the study. Multivariate logistic regression was performed to explore the potential risk factors for LBW and PD. Result: Out of 416 singleton infants born to HIV-infected mothers, the prevalence of LBW and PD was 89 (21.4%) and 69 (16.6%), respectively. The baseline maternal CD4 counts below 200 cells/mm3, maternal body mass index (BMI) below 18.5, maternal anemia and maternal exposure to Highly Active Antiretroviral Treatment (HAART) were factors significantly associated with LBW. On the other hand, a baseline maternal CD4 level below 200/ mm3, having no Prevention of Mother-to-Child Transmission (PMTCT) intervention during pregnancy, maternal BMI less than 18.5, maternal Eclamsia during pregnancy, and mothers being on HAART before pregnancy were factors associated with preterm delivery. Conclusion: There was a significant prevalence of low birth weight and preterm delivery among infants born to HIV-positive mothers. The programme for PMTCT services should maximize the need for an early identification of those mothers with predicted complications.