Indeed, when examining the factors associated with loss to follow-up during follow-up, we found that ‘‘younger age (i.e., 18–21 years),’’ ‘‘HIV-positive status at entry,’’ ‘‘less than university education,’’ ‘‘recreational drug user,’’ and having a history of HIV testing were associated with being classified as lost to follow-up (data not shown). These findings suggest that the profile of the participants who missed visits or were lost to follow-up is similar to that of high-risk sexually active young Thai MSM.Achieving effective and sustainable programs, i.e., youth-friendly services, is crucial to adequately serving HIV-positive youth.