This study aimed to assess levels of ART adherence and to examine the relationship between adherence and treatment outcomes. A longitudinal study in Hunan and Hubei provinces used the CPCRA Antiretroviral Medication Self-Report and a 7-day Visual Analogue Scale to assess levels of adherence, while quality of life was evaluated using SF-36. CD4 cell count and the number, duration, and cost of hospitalizations were collected from participant medical records. Measurements were obtained at baseline, month 3, and month 6. A total of 113 participants enrolled and 98 completed the study. The mean level of adherence was 91%, 89%, and 88% at baseline and at 3 and 6 months, respectively. Of participants, 54/98 (58%) reported taking all doses at all three interviews and were classified as consistent adherers (CA). CAs had better physical function (p = 0.001), general health (p = 0.009), vitality (p = 0.016), social functioning (p = 0.001), and mental health (p = 0.023), and presented a higher CD4 cell count (p = 0.028). CAs also had fewer hospital admissions and readmissions (p = 0.005), shorter hospital stays (p = 0.005), and lower hospital expenses (p = 0.006). Consistent adherence is associated with better outcomes including improved quality of life, higher CD4 counts, and lower health care costs.