We performed a retrospective and observational study of 51 patients treated with tigecycline, as the treatment for nosocomial infections due to multidrug-resistant microorganisms, to evaluate the superinfection rate and their etiologies. Superinfections were diagnosed in 12 (23.5%) patients (seven due to Pseudomonas aeruginosa, 13.7%) and one patient had P. aeruginosa colonization. Five patients with superinfection died (41.6%), three due to superinfections and two to underlying diseases. The superinfection rate observed during tigecycline treatment is higher than that previously reported. Pseudomonas aeruginosa is the most frequent agent, being the cause of 58.5% of all superinfections.