No data currently exist to define normal bladder compliance (C) in women. This study was undertaken to establish normative data for C in neurologically intact women and to determine if detrusor instability (DI) is associated with changes in C. The multichannel urodynamic tracings of 270 patients (195 stable, 75 unstable) were reviewed according to a standard written protocol. Vesical and abdominal pressures (Pves, Pabd) were measured during retrograde filling after a stable baseline was established (<50 ml) and just prior to cessation of infusion. If a detrusor contraction occurred, measurements were taken during a 5-sec window preceding onset of contraction. The vesical volume used to calculate C was the total bladder volume determined by completely emptying the bladder at the end of cystometry. Compliance was calculated by dividing this volume by the change in detrusor pressure (Pdet). For the purpose of some analyses, infinite C, i.e., no observed rise in Pdet, was arbitrarily assigned a value of 1,000. Overall, 47.6% of women had no increase in Pdet with filling to maximum cystometric capacity (MCC) and had infinite C. Women with instability were significantly less likely to have infinite C than those with stable bladders (32% vs. 53%; P = 0.003). In 75% of women, C was >130 mUcm; in 90%, C was >60 mUcm; and in 95%, C was >40 mUcm. There were significant differences between the distribution of stable and unstable bladders above and below each of these percentile cutoffs. Only 2 women, both of whom had unstable bladders, had C <20 ml/cm water. Ninety-five percent of neurologically intact women have C >40 ml/cm, and nearly half have no increase in Pdet during filling to MCC. Patients with DI have significantly less compliant bladders than do those with stable bladders. If C is <40 ml/cm, a woman is 16 times more likely to have DI. Decreased C may suggest the diagnosis of DI in patients with urge incontinence whose symptoms are not reproduced in the laboratory.