Background: The success of Anti Retroviral Treatment (ART) is highly dependent onrnadherence to complex ARV regimens. Unfortunately, up to 25% of patients discontinuerntheir initial HAART regimen mainly because of toxic effects.rnObjectives: To assess the magnitude of adverse drug reactions (ADRs) and associatedrnfactors among patients on Anti Retroviral TreatmentrnMethods: Out of the source population that consisted of 3240 adult AIDS patientsrnstarted on ART at Zewditu Memorial Hospital from January 2004 to December 2005, 554rnstudy subjectsâ€™ clinical records were selected using systematic random samplingrntechnique. The study was an institution based cross sectional study conducted usingrnreview of clinical records of adult patients on ART to examine the status of ADRs andrnfactors associated with it among patients on ART. Independent predictors of therndevelopment of ADRs, types and severity were assessed with binary logistic regression.rnResults: Out of the total of 554 clinical records, 526 (94.9%) were reviewed. At least onernof the drugs was changed in 120(22.8%) of the patients. There were 73 (13.7%) lost forrnfollow up. The main reasons for changing ARV drugs were toxicity/side effects 97(81%)rnfollowed by illness in 14(12 %), and pregnancy in 4(3%). The frequency of ADRs wasrn124(24%). The most frequently diagnosed ADRs were Anemia 42(33.9%) followed byrnPeripheral Neuropathy 35 (28.2%) and Elevated ALT 31(25%). Majority 94(75.8%) of thernADRs were classified as grade III. Variables associated with ADRs were regimenrncontaining NEV (OR=1.60; CI=1.04-2.47), treatment durations 6-10, 11-15 and >15rnmonths OR 3.50 (1.47, 8.33), 3.36 (1.34, 8.40) and 5.08 (2.20, 11.75) respectively andrntaking other drugs (OR=1.80; CI=1.06- 3.03).rnConclusions: Relatively very high rate of changing of drugs was noted with in first linernregimen drugs, with high lost to follow up rate which may shorten the durability of the firstrnline regimen. The most frequent ADR was anemia followed by Peripheral Neuropathyrnand Elevated ALT. The type of ADRs that the patient developed was very muchrnassociated with the duration of treatment and the regimen. Therefore, early diagnosisrnand appropriate management of ADRs is reckoned to decrease the rate of changing firstrnline drugs which eventually maintain their efficacy and durability.