Intravascular catheters are indispensable in modern medical practice; healthcare institutions purchase millions of them each year. The present study describes an outbreak of Pseudomonas aeruginosa catheter-related bloodstream infection (CRBSI) in a medical ward of the associated hospitals, a teaching hospital with 1005 beds, in Ancona, Italy, with details of the source of infection and the efficacy of the control measures adopted. The environmental strain of P. aeruginosa was isolated from the mixture of heparin and saline solution. Clinical and environmental isolates were identical at PFGE, showing that the outbreak had been caused by a single clone of P. aeruginosa. The frequency of P. aeruginosa bacteraemia depends on the population of patients studied; our patients did not show risk factors that increased their susceptibility to hospital infections. As these pathogens cannot be eradicated from the hospital environment, constant infection control measures are needed in order to prevent nosocomial infections.