Long-term diagnosed and treated HIV-infected patients have to cope with a wide range of challenges that threaten their ability to age successfully. We report the results of a randomized controlled trial testing the effects of a mindfulness-based cognitive therapy (MBCT) program on quality of life (QoL), emotional status, and immune status over a 3-month period. Forty HIV-infected patients diagnosed prior to 1996 and on cART for a minimum of 5 years were randomized to follow an MBCT program (n = 20) or remain as controls (routine follow-up) (n = 20). A regression analysis was performed, and the measurement of effect size was estimated using Cohen’s d. QoL, psychological stress, depressive symptoms, and anxiety symptoms improved in the MBCT group compared with the control group. During follow-up, patients in the MBCT group had a significantly increased CD4 cell count. Effect sizes for MBCT on the variables assessed were large (d = 0.8). The findings suggest that this program may help to promote successful aging in these patients.