Transrectal ultrasound (TRUS)-guided prostate biopsies are among the most common outpatient diagnostic procedures performed in urology clinics, with an estimated 624,000 performed annually in the United States (CDC, unpublished data, 2006). The procedures generally are performed in follow-up to elevated levels of prostate-specific antigen or abnormal digital rectal examinations. Septicemia has been reported as a rare complication of the procedure. This report summarizes an investigation of four cases of Pseudomonas aeruginosa infection after TRUS-guided prostate biopsies in which contamination of the equipment was the likely source. The findings underscore the need to adhere to recommendations for the cleaning and disinfection of TRUS-guided prostate biopsy equipment.