Q fever is a widespread disease caused by the rickettsia Coxiella burnetii, an obligate intracellular bacteria which man usually acquires through the inhalation of infected dust from subclinically infected animals. Q fever may be acute or chronic. The chronic form mostly presents as endocarditis, which is difficult to diagnose and may ultimately be fatal. Immunocompromised conditions and underlying heart disease are the most important risk factors to consider in cases of Q fever endocarditis. The ultimate diagnosis is based on specific diagnostic tests which include serology, demonstration of C. burnetii in valvular material, isolation of C. burnetii from blood and tissue samples by cell-culture techniques as well as amplification and detection of the bacterial DNA by polymerase chain reaction. Treatment of chronic Q fever endocarditis is complex and requires long-term antibiotic therapy, sometimes associated with heart valve replacement. At the present time neither an optimal antibiotic combination nor the duration of treatment is known and patients with Q fever endocarditis require prolonged follow-up because of the possibility of later relapses.