Background: Substantial progress has been made in the management of pediatric HIV infection in Ethiopia with the implementation of mother-to-child-prevention programs. Since the introduction of HAART in 2005, mortality among HIV-infected children has reduced while the rate of hospitalization was expected to rise. The purpose of this study, therefore, was to assess predictors of hospitalization in children on ART in seven university referral hospitals in Ethiopia.Methods: A prospective cohort study design was employed on children age 0-18 years as part of a multisite observational study.  ART-experienced eligible and ART-naïve children with HIV/AIDS were enrolled into the Advanced Clinical Monitoring (ACM) till December 31, 2012 were included. From the database, information on hospitalization and other independent variables were extracted. Analysis was done using both SPSS for Windows version 16.0 and STATA. Descriptive analyses and modeling was done using logistic regression.Results: Of the 405 children on ART (174 experienced, 231 naive), 86 (20.7%) were hospitalized for various reasons; two children were excluded since they were hospitalized for unrelated conditions (appendicitis and burn). Fifty one (60.7%) of the eighty four admitted children were hospitalized in the first six months of ART initiation. Of the independent variables, only the presence of opportunistic infections and duration on ART were significantly associated with hospitalization both on bi-variable and multivariable analyses (P-value <0.05). As the duration on ART increased by one month, the risk of hospitalization decreased by 5.4%, which is statistically significant (P < 0.001). Whereas the incidence (number) of OI’s increased by one, the risk of being hospitalized increased by 35.2% (P = 0.002). Of the individual opportunistic infections, pneumonia was found to be the only predictor of hospitalization (P-value = 0.002).Conclusion: This study showed that nearly two-third of the hospitalization was within 6 months of initiation of ART; and presence of OI and duration on ART were the only predictors of hospitalization. Key words: Hospitalization, Children, HIV/AIDS, HAART