The aim of this prospective study was to evaluate the morbidity of invasive urodynamic study (UDS) in type 2 diabetic patients. Study was conducted on 94 diabetic (59.4 +/- A 0.8 years) and 110 non-diabetic (58.1 +/- A 0.9 years) patients who had lower urinary tract symptoms. All patients underwent pressure-flow study. The major complication rate after UDS, including urinary tract infection, fever, urinary retention and gross hematuria, was 11.8% for non-diabetics and 22.3% for diabetics (p = 0.044). No significant differences were found between diabetics and non-diabetics according to gender with respect to dysuria, hematuria and pain (p > 0.05). Existence of pyuria before UDS was significantly higher in diabetic women with major complication than without major complication (p = 0.011). On the other hand, residual urine volume (p = 0.004) and diabetic cystopathy (0.005) were found significantly higher in diabetic men with major complication than without major complication. Our study demonstrated that UDS has an important role on the occurrence of high objective and subjective morbidity in diabetic and non-diabetic patients. Therefore, UDS indication should be carefully evaluated, especially in diabetic men who have high residual urine volume and diabetic women who have pyuria before UDS.