The aim of this study was to investigate, in a group of geriatric inpatients with established incontinence, the relationships among urine loss, voided volumes, frequency of voiding, and fluid intake. The investigated included 128 patients: 76 women and 52 men, with a median age of 79 years. One-half had significant cognitive impairment. Patients underwent 24-hr monitoring of fluid intake, urine loss, and voiding, as well as conventional videourodynamic testing. Diurnal and nocturnal voiding frequencies were significantly but relatively weakly related to fluid intake. Diurnal and nocturnal voided volumes were more closely related, however, to the fluid intake. There was a strong and easily interpretable relationship among nocturnal voided volume, nocturia, cystometric bladder capacity, and evening fluid intake. Sixty of 128 patients had urodynamically proven urge incontinence, and this group was studied separately. They were more cognitively impaired and had significantly greater urine loss and smaller fluid intake than was true of the other incontinent patients. Urine loss was significantly related to fluid intake in this group. Nocturnal urine loss increased by an average of 28 ml/dl of evening fluid intake and decreased by 17 ml/dl voided at night. These results suggest that nocturnal toileting and evening fluid restriction may reduce nocturnal urine loss by a small but useful amount in carefully selected older patients with severe urge incontinence. © 1993 Wiley-Liss, Inc.