The symptomatology and urodynamic findings of 318 male patients (45–84 years) with suspected bladder outflow obstruction have been analysed. Inflow cystometry showed that 57% of patients had unstable bladders and a pressure flow analysis of micturition that 67% had obstructed micturition. The symptoms of urgency, urge incontinence and frequency were associated with bladder instability and not with obstruction. The symptoms of hesitancy and slow stream were significantly related to obstruction. Post-micturition dribble and nocturia were related to neither urodynamic finding in this series.