No tool is available to diagnose drug-induced pemphigus (DIP) and to predict its outcome after the withdrawal of the culprit drugs. This retrospective pemphigus case series study compared cutaneous/mucosal immunostaining of a monoclonal antibody directed toward desmogleins 1 and 3 (32-2B) in 37 patients with DIP and 56 patients with idiopathic pemphigus. There was a significant difference between the groups in terms of pruritus, superficial form, mucosal involvement, and circulating antibodies. 32-2B staining disclosed a patchy pattern in 47 (84%) of idiopathic pemphigus cases and in 11 (30%) of DIP cases (P<.0001). A normal pattern, used as a diagnostic test for DIP, had 70.3% sensitivity (95% confidence interval [CI], 53.0-84.1), 83.9% specificity (95% CI, 71.7-92.4), a 32.7% positive predictive value, and a 97.9% negative predictive value. Of 17 patients with DIP with a normal pattern of 32-2B, 14 recovered, whereas only 2 of 9 patients with DIP with a patchy pattern recovered (P<.005).32-2B immunolabeling is useful for diagnosing DIP and is an indicator of a good prognosis.