Objective: To determine socio-cultural, demographic and highly active antiretroviral therapy (HAART) program-related factors associated with immunological failure (IF) among clients on HAART in Dar es Salaam care and treatment clinics. Methods: A 1:2 matched case control study was done from February to April 2012 in HIV/AIDS care and treatment clinics in Dar es Salaam. Data were collected from National AIDS Control Program (NACP) data base and patient's charts to obtain 60 sets of study participants who were interviewed using the structured questionnaire. Data analysis was done by using EPI Info 3.5.1 version. Results: The mean age of all study participants was (42.00±9.07) years with 35% (63) being males. History of poor antiretroviral therapy (ART) adherence due to exposure to drug holiday with loss to follow up (OR=11.96; 95% CI=2.07–69.26), history of changing care and treatment clinics (OR=12.07; 95% CI=2.10–69.27) and the lack of treatment supporter (OR=23.26; 95% CI=1.85–291.66) were found to be strongly associated with the occurrence of first line HAART-IF. Conclusions: HAART-IF in Dar es Salaam is associated with ART programmatic and patients' centered challenges. There is a need to review the approaches on ensuring ART adherence, clients follow up and referral system so as to reduce the incidence of IF as we move to a more decentralized peripheral drug picks clinical initiative.