In order to provide an overview of nosocomial infections due to Pseudomonas by hospital service on which they occur, site of infection, and age of patient, data were analyzed on 544 such infections collected through a collaborative surveillance program in community hospitals. About seven of every 1,000 hospitalized patients developed an infection with Pseudomonas aeruginosa, which accounted for about one-tenth of all nosocomial infections. The urinary tract was the most common site of infection. The highest rates of infection occurred in patients in burn units. Very young and very old patients had higher rates of infection overall than did other age groups, but the risk of infections in different sites changed significantly with age. Exposure and host susceptibility factors appear to underlie the characteristics observed regarding hospital service, site of infection, and age of patients with infections due to Pseudomonas.