Magister Public Health - MPH / Background: First line regimens give patients the best chance of long-term treatment success. It is imperative that patients stay on their original first line regimens to ensure program viability. As the ART programme matures in Namibia the proportion of patients who have had their first line regimens modified continues to increase. It is estimated that 3.1% of adults in Namibia are on second line regimens. Second line or other modified regimens are generally reserved for clinical, immunological or virological failure and toxicity related complications. These modified regimens often involve a higher pill burden, more toxicities and are often more expensive. A more detailed understanding of the factors associated with first line regimen modification could allow healthcare providers in Namibia to target these factors for intervention to reduce regimen modification and improve treatment outcomes. Methodology: This quantitative descriptive retrospective cohort study sought to describe factors associated with first line HAART regimen modification in treatment naïve adult patients who started HAART at Gobabis State Hospital between 1st January 2007 and 31st December 2010. Utilizing data from an existing electronic patient management system, quantitative methods were used to assess the prevalence, reasons and factors associated with first line HAART regimen modification. Results: The prevalence of HAART regimen modification was 14.1%. Treatment toxicity was the major reason (35%) for HAART regimen modification and this was largely due to D4T containing regimens. This was followed by treatment modification due to concurrent TB disease (27.3%), new drug availability (19%), pregnancy (6.6%) and virological failure (2%). A death rate of 9% was recorded by the end of the study period in each of the two groups, of those who had their first line HAART regimen modified and those who remained on original regimens respectively. There were statistically significant associations between regimen modification and type of regimen, care entry point, duration from HIV diagnosis to entry into HIV care, sex and functional status. Regimen modifications resulted in more AZT and TDF based regimes while 88.7% of patients had D4T taken off their HAART regimens. Conclusions: HAART regimen modification at Gobabis State hospital is lower than in other settings was largely due to treatment toxicity. The death rate is high and warrants further exploration. Regimen modifications resulted in more AZT and TDF based regimes and more patients had D4T taken off their HAART regimens. Recommendations: Patients still on D4T need close monitoring for side effects associated with this drug and should be promptly changed if this is the case. This study raises the important programmatic issue of the need for good data collection practices. HIV positive patients who are pregnant and those with concurrent TB disease need close monitoring to ensure that HAART regimens are modified appropriately.