Syphilis is a disease caused by Treponema pallidum infection with protean clinical manifestations. Musculoskeletal complaints are however uncommon and most of the time mild. Occasionally they can dominate the clinical picture and simulate a variety of rheumatic diseases. The authors present the clinical case of a 33-year-old woman who developed a lupus-like syndrome in the postpartum, characterized by polyarthritis, elevated acute phase reactants and positive antinuclear antibodies (ANA). Physical examination revealed a macular non-pruriginous skin rash involving the trunk, upper limbs and palms. The Rapid Plasma Reagin (RPR) and Treponema Pallidum Hemaglutination (TPHA) tests gave a positive result and the patient was diagnosed as secondary syphilis and medicated with 2.4 MU of benzathine penicillin intramuscular weekly for 3 weeks, with complete resolution of clinical signs and ANA negativation. The association of rash and arthritis may occur in several rheumatic diseases but in the presence of palmoplantar involvement, the possibility of syphilis infection should not be overlooked.