Three familial cases of psittacosis are reported. The first case was a 46-year-old woman, the second case, her 18-year-old daughter. Both of them often visited the house of the third case, a 49-year-old women, who was the elder sister of case 1 and who took care of the chick of a budgerigar which she kept in the house. Case 1 came to our hospital with abrupt onset of fever, headache, nausea and general malaise. Because she was suspected to have meningitis, she was admitted to the Department of Neurology. On admission, her chest X-ray film showed bilateral ground glass shadows. She also had hypoxemia and liver dysfunction. On learning of her history of contact with the chick, psittacosis was suspected. Case 2 suffered from fever and headache. Her chest X-ray film revealed opaque infiltration in the right lower lung field. Case 3 complained of fever, headache and vomiting. Her chest X-ray film showed fan-shaped faint shadows in the left upper, middle and lower lung fields. We interpreted these findings as showing psittacosis based on anamnesis. The result of the complement fixation (CF) antibody titer against chlamydia was 1:32 in cases 2 and 3, enabling a serological diagnosis of psittacosis. The corresponding result was 1:16 in case 1. Although the CF antibody titer showed no increase, we diagnosed the case clinically as psittacosis. It is difficult to correctly diagnose psittacosis only from the physical findings and chest X-ray films. Detailed anamnesis, in particular taking a history of exposure to birds, is an important clue for diagnosis.(ABSTRACT TRUNCATED AT 250 WORDS)