Endocarditis is a rare, but some times fatal, complication of Q fever. Its diagnosis is difficult and it is based on non-specific cardiac findings and a high title of phase I antibodies. The treatment is based on tetracyclines alone or in combination with cotrimoxazole, for long periods of time. The therapeutic efficacy is evaluated by the measurement of phase I antibodies, every three months. The relapses are frequent despite the long period of antibiotic therapy. We report what is probably the first case of Q fever prosthesis endocarditis in Portugal, as a complication following an acute episode of Q fever.