This mixed methods pilot study examined the feasibility, acceptability, and impact of a web-based gratitude exercise (the ‘Three Good Things’ exercise (TGT)) among 23 adults in outpatient treatment for alcohol use disorder. Participants were randomized to TGT or a placebo condition. The intervention was feasible with high rates of completion. Participants found TGT acceptable and welcomed the structure of daily e-mails; however, they found it difficult at times and discontinued TGT when the study ended. Participants associated TGT with gratitude, although there were no observed changes in grateful disposition over time. TGT had a significant effect on decreasing negative affect and increasing unactivated (e.g. feeling calm, at ease) positive affect, although there were no differences between groups at the 8 week follow-up. Qualitative results converged on quantitative findings that TGT was convenient, feasible, and acceptable and additionally suggested that TGT was beneficial for engendering positive cognitions and reinforcing recovery.