A hundred years have elapsed since the first isolation of Pseudomonas aeruginosa. Most of the early infectious processes were uncommon, but experimental studies of pathogenesis anticipated recent work. Today we recognize P. aeruginosa as a pathogen of major importance in immunocompromised patients, patients with cystic fibrosis, and patients with breached anatomic defenses. Multiple virulence factors have been identified that may account for, possibly in concert, the ability of this organism to cause disease even in normal hosts. Immunologic approaches to control or treatment offer some promise, as does the development of new antibiotics. The outlook for treatment and control of infections due to P. aeruginosa seems dependent on better understanding of pathogenesis, improved understanding of host defenses, and the most advantageous use of new antimicrobial agents.