This study investigates the survival from the time of diagnosis to death of 98,876 men and 57,316 women between the ages of 15 and 96 years who received medical care at public and private hospitals in Thailand after being diagnosed with symptomatic HIV-positive or AIDS between 2000 and 2005 from all regions of Thailand. Using a retrospective cohort study, risk ratios (RR) and 95% confidence intervals (CI) are estimated by the Cox proportional hazards model adjusting for age, gender, marital status, occupation, region of residence, and year of diagnosis. Significant increased risk of mortality is observed for patients diagnosed with AIDS as compared to those with symptomatic HIV-positive, the risk being approximately twofold for men (RR=2.37, 95% CI=2.27, 2.47), almost threefold for women (RR=2.85, 95% CI=2.69, 3.02), and more than threefold for women in the 15-24-year age group (RR=3.36, 95% CI=2.83, 3.98). The risk also varied from being twofold in the northern region of Thailand (RR=2.23, 95% CI=2.11, 2.35) to being threefold in the northeast (RR=3.05, 95% CI=2.79, 3.32). Our findings of increased risk of mortality for subgroups of the population suggest the need for sustained attention to HIV prevention efforts with support from society at large, and to the early diagnosis and treatment of these patients, especially women and youth.