Background: -Treatment of HIV infected patients with Highly Active Antiretroviral Therapy (HAART) leads to immune reconstitution as shown by increase in CD4+ lymphocyte counts, decreased risk of opportunistic infection and improve survival, however, little is known about its impact on hematological parameters in resource limited settings like Ethiopia.rnObjective: -To assess hematological profile among adult HIV infected individuals at the baseline and six month after initiation of Highly Active Antiretroviral Therapy.rnMethods: -Retrospective cohort study was conducted among HIV infected adult patients who attended ART clinic and received HAART between September 2005 and August 2010 at ART clinic of Black Lion Specialized Hospital Addis Ababa, Ethiopia. A total of 379 subjects were selected based on convenience sampling. Demographic, clinical and hematological (WBC, CD4+ T cells, Hgb and Platelets) data were collected between July and August 2010 carefully from the existing ART logbook and patient follow up cards accordingly.Selected hematological abnormalities were defined as leucopenia, thrombocytopenia, severe thrombocytopenia, anemia and immunodeficiency. Data collected through a standardized questionnaire were entered into Excel spread sheet and transported into and analyzed by SPSS Version 15.0 soft ware (SPSS INC, Chicago, IL, USA).Median change of different hematological values during follow up time between consecutive visits and each follow up from the base line were compared using Wilcoxon signed rank test.rnResults: -At the baseline 379 subjects who started ART from September 2005 to August 2010 were included in the study; 240 of the patients were females. The subjects studied had a baseline CD4+ T cells count ranging from 4-573 cells/ul, median 111 cells/uL IQR (72-176). 329 (86.8%) of the study subjects were having CD4 + T cell count below 200 cells/ul and CD4+ T cell count of