Ten spinal cord injured patients aged 8 to 55 years (mean 32) were followed for up to 2 months after admission to a rehabilitation setting from an acute care hospital. Urinary fluid and bladder epithelial cells were collected weekly by intermittent catheterization and examined for bacterial colonization. Six patients had no history of urinary tract infection upon admission, likely due to the antimicrobial coverage given during acute care. All the patients subsequently became colonized with uropathogens at some time during the study period. Bacterial biofilms were found in 73% of the samples (73% Gram negative organisms, 27% Gram positive), with mean pathogenic adhesion counts of 29 organisms per bladder cell. In 16% of cases, bladder biofilms were found when urine culture was negative. Bacterial biofilms were also evident during antimicrobial therapy in 10 of 12 samples tested and urine cultures showed breakthrough infections in 50% of cases. Two asymptomatic patients were colonized with Klebsiella pneumoniae and Pseudomonas aeruginosa and were dismissed without requiring therapy. Clearly, bacterial biofilms can exist on bladder epithelia, without being detected in urine samples and without giving rise to symptoms. The extent to which they occur and damage the host remains to be determined, as does the answer to the question, should these patients be treated?