A prospective study was made of clinical symptoms, liver function and pregnancy prognosis in women with cholestasis of pregnancy (CP). We used several positive and negative criteria to allow a clinical definition of CP as itching limited to time of pregnancy with or without laboratory evidence of liver dysfunction. The incidence during 1971-74 was 1.5% (100/6798 women) and lower during 1980-82 (52/5441 = 1.0%). One hundred consecutive pregnant women without itching were used as clinical controls. The incidence of CP showed a distinct seasonal variation, culminating in November. Women with CP had often had itching during previous pregnancies and during use of contraceptive pills and described anamnestically itching in mother and sisters. Laboratory data in CP were compared with reference intervals for healthy pregnant women. Serum enzyme levels were significantly increased for serum alkaline phosphatase, 5-nucleotidase, aspartate aminotransferase and alanine aminotransferase in the second and especially in the third trimester. The enzyme distribution was often markedly skewed to the right, i.e. some patients reacted more than others. Most patients with cholestasis only had itching without pronounced abnormalities in laboratory data. This mild form of CP was associated with a good prognosis for both mother and child.