A report is given of a 22-year-old male with life-long pronounced jaundice. Serum bilirubin was found fluctuating between 10 and 15 mg% , all of which was conjugated, as determined with a modification of the van den Bergh technique. Liver function tests, including BSP-elimination and oral cholecystography, were normal. The liver biospy specimen showed normal structure of the liver lobule and moderate amounts of light brown pigment granules in the parenchymal cells near the central vein. Electron microscopy showed these granules to be indistinguishable from the pigment found in chronic idiopathic jaundice. A thorough study of the patient''s family, including personal examination of 35 members, failed to disclose secondary cases, with the possible expection of the proband''s deceased sister. The case demonstrates that features of the different syndromes of constitutional hyperbilirubinemia may exist in the same patient, and that differentiation therefore may be uncertain. It is suggested that at the present time absence or presence of conjugated bilirubin in the serum, determined by a reliable technique, is the only safe criterion of differentiation, separating constitutional defects in the elimination of bilirubin before and after the conjugation process has taken place ("pre-conjugation" and "post-conjugation" blocks).