A review was conducted in Haiti to determine the timing and outcome of active tuberculosis (TB) in human immunodeficiency virus (HIV)-positive patients who had previously received isoniazid (INH) prophylaxis. Of 1005 HIV-seropositive patients who completed INH prophylaxis, 14 (1.4%) subsequently had active TB diagnosed. The median interval between discontinuation of INH prophylaxis and TB diagnosis was 8 months for 6 patients receiving 6 months of INH, 22 months for 5 patients receiving 12-24 months of INH, and 40 months for 3 patients receiving 24-36 months of INH (P = .026). There is a postprophylaxis effect on INH that is dependent upon the duration of therapy.