The authors review critically such parameters as symptomatology, post-micturition residual urine, bladder trabeculation and uroflowmetry that in the actual state of the art appear more accredited in the evaluation of lower urinary tract obstruction. All have some interpretative limits. However, uroflowmetry appears to be the most reliable and for this reason it is the first step in the study of suspected infravesical obstruction. It can discover equivocal situations in which pressure-flow studies only supply diagnostic help in order to avoid false diagnosis of infravesical obstruction and useless therapeutic approaches.