Technologic advances have allowed a means for more precise measurement of cutaneous bilirubin. These advances have led investigators to examine the correlation between cutaneous and blood bilirubin in hopes of either replacing or reducing the number of serum bilirubin values obtained. In the past other investigators attempted to do the same, using visual estimates of jaundice with and without the help of reference devices. The establishment of an acceptable correlation between cutaneous and serum bilirubin requires (1) accurate measurement of serum bilirubin, (2) accurate measurement of cutaneous bilirubin, and (3) steady-state conditions between the blood-cutaneous bilirubin "compartments." The accuracy with which cutaneous bilirubin can be measured appears similar or better than that with which serum bilirubin is measured; with older transcutaneous devices significant interobserver variability may exist. Bias in the form of other skin chromogens also interferes with accuracy. Rapid changes in serum or cutaneous bilirubin concentration or nonhomogeneous distribution of cutaneous bilirubin interferes with our knowledge of cutaneous-blood bilirubin kinetics. At present transcutaneous bilirubinometry cannot replace routine serum measurements, but both new and old transcutaneous devices can serve as effective screening devices. The choice of which device to use depends on its cost-effectiveness in any given clinical setting.