This disease is characterized by a mild and predominantly conjugated hyperbilirubinemia. Normally, bilirubins range between 2 mg/dl and 5 mg/dl. More than half of the bilirubin is direct. Other liver function tests are  unaffected. This disease is often unmasked after puberty, and the degree of jaundice will increase with associated intercurrent illness, use of oral contraceptives, or pregnancy. This syndrome is seen more frequently in Persian Jews and is associated with a deficiency of coagulation factor VII. It should be noted that although there is an increased frequency in Persian Jews, this disease has been reported in all races and in both sexes.

Urinary coproporphyrin excretion studies have been able to differentiate this disease from other hepatobiliary disease processes. Coproporphyrin exists in different isomeric forms in body fluids. Isomer I is a byproduct of heme metabolism, whereas isomer III is a precursor of heme. Urinary coproporphyrin excretion is not increased in Dubin-Johnson syndrome; however, in other hepatobiliary diseases, the coproporphyrin isomer is predominantly III, but in Dubin-Johnson syndrome measurement of isomer I greater than 80% is considered diagnostic of Dubin-Johnson syndrome.