Pill counts with calculated adherence percentages are used in many settings to monitor adherence, but can be undermined by patients discarding pills to hide nonadherence. Pill counts suggesting that >100% of prescribed doses were taken can signal "pill dumping." We defined "overadherence" among a cohort of 300 HIV-infected adolescents as having greater than one-third of pill counts with >100% adherence during a year of follow-up. Apparent overadherence was more common in those with virologic failure than in those with suppressed viral loads (33% vs 13%, χ(2) P = 0.001). Pill count adherence repeatedly >100% may identify HIV-infected adolescents at increased risk of treatment failure.