Data regarding the prevalence and urodynamic characteristics of involuntary detrusor contractions (IDC) in various clinical settings, as well as in neurologically intact vs. neurologically impaired patients, are scarce. The aim of our study was to evaluate whether the urodynamic characteristics of IDC differ in various clinical categories. One hundred eleven consecutive neurologically intact patients and 21 consecutive neurologically impaired patients, referred for evaluation of persistent irritative voiding symptoms, were prospectively enrolled. All patients were presumed by history to have IDC, and underwent detailed clinical and urodynamic evaluation. Based on clinical evaluation, patients were placed into one of four categories according to the main presenting symptoms and the existence of neurological insult: 1) frequency/urgency; 2) urge incontinence; 3) mixed stress incontinence and irritative symptoms; and 4) neurogenic bladder. IDC was defined by detrusor pressure of ≥ 15 cm H2O whether or not the patient perceived the contraction; or < 15 cm H2O if perceived by the patient. Eight urodynamic characteristics of IDC were analyzed and compared between the four groups. IDC were observed in all of the neurologically impaired patients, compared with 76% of the neurologically intact patients (P < 0.001). No correlation was found between amplitude of IDC and subjective report of urgency. All clinical categories demonstrated IDC at approximately 80% of cystometric capacity. Eighty-one percent of the neurologically impaired patients, compared with 97% of the neurologically intact patients, were aware of the IDC at the time of urodynamics (P < 0.04). The ability to abort the IDC was significantly higher among continent patients with frequency/urgency (77%) compared with urge incontinent patients (46%) and neurologically impaired patients (38%). In conclusion, when evaluating detrusor overactivity, the characteristics of the IDC are not distinct enough to aid in differential diagnosis. However, the ability to abort IDC and stop incontinent flow may have prognostic implications, especially for the response to behavior modification, biofeedback, and pelvic floor exercise. Neurourol. Urodynam. 20:249–257, 2001. © 2001 Wiley-Liss, Inc.