Transient worsening of tuberculosis (TB) symptomatology and lesions in response to anti-TB therapy has previously been reported as paradoxical worsening. Recently, paradoxical worsening of TB following antiretroviral therapy in AIDS patients was reported. However, paradoxical worsening of nontuberculous mycobacterium, including Mycobacterium abscessus (M. abscessus), has not been reported previously. We reported the first case of paradoxical worsening of pulmonary M. abscessus.