['Several conditions are considered in differential diagnosis of neonatal cholestasis. Of these the most important is extrahepatic biliary atresia (EHBA), while prompt diagnosis and surgical correction of obstruction can ameliorate clinical symptoms, provides long term survival for about one fourth of patients and serves as an important bridge to transplantation for many others. From histopathologic standpoint, features of EHBA overlaps with other diagnoses and so ancillary tests such as immunohistochemical staining for CD56 is suggested by some authors as a helpful tool in differential diagnosis.Hereby we wanted to examine this staining in our center which is a referral children hospital and to prove its efficacy in our problematic cases.', 'By retrospective review of pathology records during 2000 to 2006 in Markaze Tebbi Koodakan (children hospital related to Tehran University of Medical Sciences), we selected 17 cases of EHBA as patients and 12 cases with other diagnoses as controls, both with some degree of bile ductular proliferation in liver biopsies. EHBA cases were all proved by surgery. Four of control cases also underwent surgery but proved to have open ducts by intra-operative cholangiography. Long term follow up and other tests ruled out EHBA in other 8 cases. Hematoxylin-Eosin stains of paraffin blocks were studied again and freshly prepared sections were immunostained for CD56.', 'Bile ducts and proliferating bile ductules were strongly positive for CD56 in 6 of 17 cases of EHBA. In 7 out of 17, positivity were seen in more than two thirds of portal tracts. In controls, one case showed strong positivity and 6 out of twelve showed positivity in more than two thirds of portal tracts. The intensity and distribution of CD56 staining did not differ significantly between two groups.'] Does cD 56 staining in liver biopsies help in differentiating extrahepatic biliary atresia from other causes of neonatal cholestasis?