The initial goal of this study was to evaluate proteinuria by using the protein to creatinine (UPC) ratio of urine obtained by cystocentesis of healthy adult captive chimpanzees. Urine samples were collected by using ultrasound-guided cystocentesis from 125 (80 male, 45 female) captive chimpanzees. All samples were collected over a 17-mo time period (August 2008 to January 2010) during the animal's annual physical examination. Samples were assayed at a veterinary diagnostic laboratory. Results indicated that both age and blood contamination affect the UPC ratio and therefore alter the diagnostic utility of the UPC ratio in chimpanzees. In addition, this research establishes reference ranges by age for the UPC ratio in healthy adult chimpanzees. Chimps younger than the median age of 24.6 y have a median UPC ratio of 0.098 (range, 0 to 1.76), whereas older animals have a median UPC of 0.288 (range, 0 to 2.44). Our results likely will enable veterinarians working with chimpanzees to better evaluate their renal function.