Summary— The risk of single catheterisation in females with urinary incontinence and/or genital prolapse was studied in patients referred for urodynamic examination.

Two hundred and eighty-six single catheterisations were performed followed by a mid-stream specimen 1 week later, and in 31 of these the initial specimen contained more than 105bacteria.

Following catheterisation bacteriuria occurred in 5 (2%) of the patients with initially sterile urine.

The phenomenon of “asymptomatic bacteriuria”, “transient significant bacteriuria” and “bladder defence mechanism” is discussed.

The risk of introducing urinary tract infection in urodynamic studies is low.