Among 470 patients with acquired immune deficiency syndrome and/or human immunodeficiency virus infection (HIV/AIDS) who underwent genotype resistance testing (GRT) after the failure of therapy, 17 (3.6%) harbored the Q151M mutation. The Q151M mutation was associated with younger age, lower CD4(+) lymphocyte count, higher HIV RNA level, and treatment with >2 pre-GRT regimens. By contrast, the Q151M mutation was inversely associated with lamivudine administration. A full reversion of the Q151M mutation was observed in 5 of 5 patients who underwent treatment interruption after GRT. The reversion was followed by a response to salvage therapy in 4 (80%) of 5 patients.