Q fever endocarditis is rarely reported in North America; only four cases have been documented since 1953. In 1981-1982, five cases were identified in the Victoria General Hospital, Halifax, Nova Scotia. Four patients were from widely separated areas of Nova Scotia and one was from Prince Edward Island. Four patients with long-standing valvular abnormalities, including two with prosthetic valves, presented with recurrent febrile episodes. The fifth patient, who was previously well, had recurrent septic embolic episodes. Clinical features and laboratory findings were variable. Diagnosis by serology was confirmed in four patients by culture of Coxiella burnetii from excised tissue. Histopathology varied from nonspecific inflammatory changes to two more distinctive patterns; electron microscopy showed C burnetii in two patients. Therapy with tetracycline and trimethoprim-sulfamethoxazole was beneficial, although three patients required valve replacement for hemodynamic deterioration. Q fever endocarditis may be more common than is recognized, and serological investigations should be performed in all cases of culture-negative endocarditis.