Two immunocompromised patients with herpetic geometric glossitis, a clinically distinctive form of lingual herpes simplex virus (HSV) type 1 infection, are described. The significant features of herpetic geometric glossitis are summarized, the clinical differential diagnosis of this form of HSV infection is reviewed, and the possible pathogenesis of these lingual lesions is discussed. Both of our patients, as well as all previously described patients with this condition, had extremely painful cross-hatched, branched, and/or linear fissures on the dorsal aspect of the tongue. Symptoms promptly resolved within 1 to 2 days, and the fissures subsequently healed within 3 to 12 days after systemic acyclovir therapy was initiated. In contrast to tongue lesions of herpetic geometric glossitis, similar-appearing lingual lesions of other conditions are usually asymptomatic. The similar morphology of corneal dendrites in herpetic epithelial keratitis and linear fissures in herpetic geometric glossitis suggest the possibility that these HSV mucosal lesions may have a common pathogenesis.