Background: This study aims to describe the trends in and determinants of six month mortality and loss to follow up (LTFU) during 2005–2009 in 13 outpatient clinics in Vietnam. Method: Data were obtained from clinical records of 3,449 Vietnamese HIV/AIDS patients aged 18 years or older who initiated ART between 1 January 2005 and 31 December 2009. Mantel-Haenszel chi-square test, log rank test were conducted to examine the trends of baseline characteristics, six month mortality and LTFU. Cox proportional hazards regression models were performed to compute hazard ratio (HR) and 95% Confidence Interval (CI). Results: Though there was a declining trend, the incidence of six month mortality and LTFU remained as high as 6% and 15%, respectively. Characteristics associated with six month mortality were gender (HR females versus males 0.54, 95%CI: 0.34–0.85), years of initiation (HR 2009 versus 2005 0.54, 95%CI: 0.41–0.80), low baseline CD4 (HR 350–500 cells/mm3 versus