Corynebacterium pseudodiphteriticum has been considered a very infrequent respiratory pathogen. We report three cases of pneumonia due to C. pseudodiphteriticum, describing their clinical and microbiological features. There were two patients with pre-existing chronic respiratory disease, one of their with steroidal therapy, and other associated with endotracheal intubation. The diagnostic was made by Gram stain and quantitative cultures from respiratory tract specimens. All patients were cured after treatment with amoxicillin-clavulanate, ceftriaxone and vancomycin respectively. C. pseudodiphteriticum must be consider as a possible causal agent of pneumonia in patients with underlying respiratory disease or endotracheal intubation. Antimicrobial susceptibility testing of C. pseudodiphteriticum may be useful for correct treatment of infected patients, but beta-lactam antibiotics are an appropriate therapeutic option against this bacteria.