The diagnosis of obstetric cholestasis (OC) has serious implications for maternal, and especially fetal, health. Total serum bile acid concentration is an important investigation in any woman with itching in the absence of a rash during pregnancy. Results should be available within 1-2 working days. Pruritus plus raised total bile acids in the third trimester suggests a diagnosis of OC. Other biochemical abnormalities, usually a raised alanine aminotransferase, accompany or follow the finding of raised bile acids. Bile acids are sensitive, but not specific, markers for OC. The diagnosis is one of exclusion. The clinician should remain alert to other causes of liver dysfunction, either specific to pregnancy or not. Effective treatment is available that improves maternal biochemical indices and well-being. It is not clear whether such treatment reduces the risks to the fetus. More active management of OC pregnancies has reduced the associated fetal and perinatal mortality.