The clinical findings during a major epidemic of Q-fever which affected 415 people in the Val de Bagnes (Valais, Switzerland) in the autumn of 1983 are reported. Q-fever symptoms were evident in 191 cases but inconspicuous or absent in 224 cases. The symptoms most frequently reported were prolonged high fever, headaches, severe exhaustion, loss of appetite, cough and myalgia. Amongst disorders which accompany acute Q-fever, pneumonia and granulomatous hepatitis are very frequent, while myopericarditis and glomerulonephritis are less frequently observed. Endocarditis, a later complication of Q-fever, is a severe illness which more frequently affects patients with underlying valvular lesions. New serological techniques now permit more rapid and more accurate diagnosis of both acute and chronic Q-fever.