We describe the clinical and pathologic features of a hitherto unreported finding in patients with esophagitis: the presence of multinucleated squamous epithelial giant cells simulating viral cytopathic effect and/or dysplasia. Routinely processed hematoxylin and eosin (H&E)-stained slides of esophageal mucosal biopsies from 14 patients with both active esophagitis and multinucleated epithelial giant cells were evaluated for a variety of inflammatory and epithelial features. Clinical, endoscopic, and follow-up data were collected and correlated with the histologic findings. Immunostaining (ABC method) for cytokeratin AE1/AE3, S-100, MIB-1, herpes simplex virus 1 and 2 (HSV), cytomegalovirus (CMV), as well as DNA in situ hybridization for human papilloma virus (HPV-ISH) was performed in all cases. Electron microscopic evaluation for viral particles was performed in three cases. The study group consisted of nine men and five women (mean age 59 years; range 23-87 years; 12 white, one black, one Hispanic). Patients presented with dysphagia or odynophagia (n = 5), upper gastrointestinal bleeding (n = 5), heartburn (n = 2), or abdominal pain (n = 2). The etiology of esophagitis was attributed to gastroesophageal reflux in 10, radiotherapy in one, Candida infection in one, drug-induced (alendronate) in one, and unknown in 1. Endoscopically, seven patients had an ulcer or erosion, four erythema, two stricture formation, and one white mucosal plaques. Microscopically, all cases showed multiple multinucleated (mean three nuclei per cell, range two to nine) squamous epithelial cells (range 2 to 11 cells per biopsy) confined to the basal zone in nine of 14 cases and involving the basal and superficial epithelium in the remainder. The nuclei contained a single or multiple eosinophilic nucleoli with a perinucleolar halo, but no inclusions, hyperchromaticity, or atypical mitoses. All cases showed associated nonspecific features of active esophagitis such as ulceration, neutrophilic and eosinophilic inflammation, basal cell hyperplasia, and elongation of the lamina propria papillae. The multinucleated giant cells, in all cases, were strongly positive for cytokeratin AE1/AE3 and were negative for S-100, HSV I and II, CMV, and HPV-ISH. MIB-1 positivity was observed in all basally located multinucleated giant cells, whereas those in the more superficial layers were negative. Electron microscopy failed to show viral particles in three of three cases. After treatment, all patients demonstrated clinical improvement. Three patients in whom follow-up biopsies were performed showed no evidence of esophagitis, epithelial cell multinucleation, or dysplasia. Multinucleated epithelial giant cell changes may rarely be seen in patients with esophagitis of varying etiology and probably represent a regenerative response to injury. This feature is important to distinguish from either viral cytopathic effect or dysplasia.