Each year millions of urethral catheters are used, and the most common complication is bacteriuria. Although usually asymptomatic, this bacteriuria may be associated with fever, acute py elonephritis, bacteremia, and death, and in long-term catheterized patients, catheter obstruction, urinary tract stones, local periurinary infections, chronic renal inflammation, chronic pyelonephritis, and bladder cancer. Only two principles are universally recommended: (1) keeping the closed catheter system closed and (2) removing the catheter as soon as possible. Although in most cases controlled trials have not been performed, alternative techniques, including condom, intermittent, suprapubic, and intraurethral catheterization, seem to be associated with lower incidences of bacteriuria and its complications than urethral catheterization.