Tullio Cuzzi. Fundação Oswaldo Cruz. Instituto Nacional de Infectologia Evandro Chagas. Documento produzido em parceria ou por autor vinculado à Fiocruz, mas não consta a informação no documento.The authors present two cases of syphilis: one mimicking reactive arthritis and the other Mucha-Habermann disease. Both reports illustrate syphilis as ‘the great imitator’, a description given by Sir William Osler, and call attention to the strong need for awareness among physicians of all specialties, especially the younger ones, who are not used to seeing this increasingly prevalent disease, as it once was in the past.