HIV-positive adolescents and young adults often experience suboptimal medication adherence, yet few interventions to improve adherence in this group have shown evidence of efficacy. We conducted a randomized trial of a two-way, personalized daily text messaging intervention to improve adherence to antiretroviral therapy (ART) among N = 105 poorly adherent HIV-positive adolescents and young adults, ages 16-29. Adherence to ART was assessed via self-reported visual analogue scale (VAS; 0-100 %) at 3 and 6-months for mean adherence level and proportion >/=90 % adherent. The average effect estimate over the 6-month intervention period was significant for >/=90 % adherence (OR = 2.12, 95 % CI 1.01-4.45, p < .05) and maintained at 12-months (6 months post-intervention). Satisfaction scores for the intervention were very high. These results suggest both feasibility and initial efficacy of this approach. Given study limitations, additional testing of this intervention as part of a larger clinical trial with objective and/or clinical outcome measures of adherence is warranted.