Fifty patients with irritative voiding symptoms and a painful bladder when full were engaged in this study to clarify the role of urodynamics in the diagnosis of interstitial cystitis (IC). Patients underwent urodynamic study, cystoscopic hydrodilatation of the bladder under general anesthesia and bladder biopsy. Twenty-eight women and two men who presented with signs of glomerulations or petechial hemorrhage of the bladder mucosa were classified as having IC, while 20 women without this characteristic were classified as having non-IC. A hypersensitive urge sensation, a small bladder capacity, a lower maximal flow rate and an abnormal flow pattern were observed in both groups of patients, but no significant difference was noted. More IC patients had a lower bladder compliance than non-IC patients (p < 0.025), and the maximal bladder capacity under anesthesia was smaller in IC patients (p < 0.05). However, there does not seem to be any definite correlation to the pathologic findings, except in patients with marked bladder inflammation, in whom a small capacity and severe clinical symptomatology were found.