The exacerbation of clinical symptoms or radiological worsening of pre-existing tuberculous lesions or the development of new lesions defines paradoxical deterioration during antituberculosis therapy. This phenomenon is relatively frequent: it is observed between 6 and 30% of patients receiving antituberculous therapy. The pathogenesis is not completely clear and it is generally regarded as an abnormal immune response to the proteins released from dead bacilli. Clinical and radiological manifestations may locate in the central nervous system, lungs, pleura, lymph nodes and skin. The diagnosis is frequently difficult and outcome is most often spontaneously favourable. It is possible that the addition of corticosteroid therapy could be beneficial on the outcome of this phenomenon. In this paper we try to review the definition, pathogenesis, clinical manifestations and treatment of this pathology.