PROJECT SUMMARY/ABSTRACT The era of antiretroviral therapy has shown increasing life expectancy and decreased HIV-related deaths, leading to a growing older adult HIV population. Yet, HIV accelerates the aging process and increases risk for numerous chronic health conditions that compromise physical and mental health functioning. Further, in this context, unhealthy alcohol use is common among persons living with HIV (PLWH) and also increases risk for negative outcomes. Yet, there are few interventions to address unhealthy alcohol use in PLWH that have resulted in significant effects nor have they employed approaches that could impact these multimorbidities. Therefore, intervention approaches that may have significant impact on unhealthy drinking in PLWH are necessary, particularly if they also have the potential to affect the physical and mental health multimorbidities common in PLWH. Efforts toward addressing another highly prevalent condition among PWLH – physical inactivity and sedentariness, may prove beneficial for changing unhealthy drinking and physical and mental health functioning. To date, physical activity (PA) approaches in PLWH have primarily consisted of structured, supervised, gym-based interventions that have resulted in positive outcomes but have been limited in their reach and associated with high drop-out in this population. Here we propose an alternate paradigm – home- based, lifestyle physical activity (LPA) with mobile health-delivered components that have the potential to address existing limitations of previous approaches. LPA interventions consist of behavioral strategies that guide individuals to integrate intermittent bouts of PA in their daily routines. An added strength of the LPA approach is it may be well-suited for PLWH engaged in unhealthy drinking by providing cumulative physical and mental health effects from regular, daily PA as well as acute effects on negative affect (common among PLWH engaged in unhealthy drinking) and urges to drink via individual, brief bouts of activity. To date, LPA interventions have not been tested in PLWH. As such, through online recruitment of PLWH, we will identify 220 HIV+ unhealthy drinkers and randomize them to the 12-week LPA+Fitbit intervention or to a Fitbit Only condition. Primary outcomes will include drinks/drinking day and objectively-determined steps/day at end of treatment and 6-month follow-ups. Changes between conditions on physical and mental health functioning, alcohol-related problems, coping, PA motivation, and PA self-efficacy will be examined as secondary outcomes. In addition, to elucidate mechanisms of intervention effects, we will employ two bursts of ecological momentary assessment to obtain multiple daily measures of affect, urges to drink, alcohol consumption, and PA engagement coupled with objective assessment of PA. If the LPA+Fitbit intervention proves efficacious, our lifestyle approach using mobile health technology will directly affect the significant multimorbidity in this at-risk population of PLWH engaged in unhealthy drinking, which in turn may have significant public health impact.