The Tzanck smear, introduced by the Frenchman Tzanck, has been used for many years in the diagnosis of bullous and vesicular dermatoses especially herpes simplex, herpes zoster and varicella. Also, in the vesicular dermatoses of newborns and immunocompromised patients it is an important diagnostic aid. The Tzanck smear is easy to perform, simple, reliable (if one is experienced) and inexpensive. A quick staining can be done by Hemacolor or Diff-Quik within one minute. The Tzanck smear is certainly useful and very reliable in the diagnosis of herpes simplex and varicella-zoster infections if obtained in the vesicular stage. The sensitivity of the Tzanck smear exceeds 80%, and the specificity 90% when the investigators are experienced. A positive Tzanck smear is an especially reliable and useful diagnostic aid. However, a disadvantage is that the smear cannot differentiate between herpes simplex virus or varicella-zoster virus infections. The Tzanck smear, although old and simple, remains an important aid in the diagnosis of vesicular, pustular and bullous diseases, in particular herpes. Cytology will, however, never replace culturing or histopathology.