The aim of this study was to verify the reliability of the Tzanck test, performed by both traditional cytomorphology and the direct immunofluorescence technique, in diagnosis of oral pemphigus vulgaris. Cytologic smears were obtained from oral erosions of thirty patients with well ascertained pemphigus vulgaris. Control smears were taken from thirty patients affected by various other diseases of oral mucosa and from thirty healthy subjects. Cytologic diagnosis of oral pemphigus was based upon significant findings of acantholytic cells by cytomorphology, and of epithelial cells with pericellular deposition of IgG (which persisted after cytocentrifugation) by direct immunofluorescence. The cytomorphological test gave positive results in twenty‐eight patients with pemphigus and in one patient with herpetic stomatitis, and negative results in all other cases. The immunocytologic test gave positive results in all patients with pemphigus, and negative results in all controls. These findings indicate that the cytomorphological test may be a useful method for screening oral pemphigus, while the immunocytologic test may provide a reliable method for definitive diagnosis.