Rapid techniques for the detection of herpes simplex virus (HSV) and varicella-zoster virus (VZV) are needed for optimal therapeutic management. VZV infection poses a serious threat, especially to seriously ill patients, for instance, immunocompromised patients. We report a case of human T-cell lymphotropic virus type 1-positive leukemia complicated by atypical multidermatomal herpes zoster. Viral culture and standard serological tests failed to prove VZV infection. Herpesvirus infection was confirmed by cytodiagnosis (Tzanck test). The final diagnosis of VZV was made by immunoelectron microscopy (IEM), which can differentiate between HSV and VZV. Immunoglobulin M antibodies in serum directed against VZV were detected by IEM but not by immunofluorescence. Because IEM was able to identify virus and analyze sera in only 2 h, it is considered a valuable additional tool for the rapid diagnosis of HSV and VZV infections.