RESUMEN
Voiding dysfunction is defined as an abnormally slow and/or incomplete micturition, and can be divided in bladder outlet obstruction (BOO) and detrusor underactivity (or hypocontractility). BOO is characterized by reduced urine flow rate and increased detrusor pressure, and can be of anatomical or functional origin. Detrusor underactivity encompasses a reduced urine flow rate associated to low pressure and/or poorly sustained detrusor contraction, and its etiology is multifactorial. Lower urinary tract symptoms are classified as storage, voiding and post micturition symptoms, may be objectively quantified with specific questionnaires, and don't correlate properly with voiding dysfunction. Patients' evaluation requires a directed physical examination of the abdomen, pelvis and genitals focused to detect anatomical and neurological abnormalities. Voiding dysfunction can be demonstrated non-invasively using uroflowmetry and pelvic ultrasound. Uroflowmetry allows determining urinary flow characteristics and their most important parameters are voided volume, maximum flow rate and shape of the curve. Pelvic ultrasound permits to estimate prostatic size and post void residual, suspect detrusor hypertrophy (due to BOO) and detect bladder stones. Invasive test must be reserved for special cases of confirmed voiding dysfunction: cystoscopy when there is concomitant hematuria, urethrocystography to study urethral stenosis and urodynamics to differentiate BOO from detrusor underactivity. (AU)