In the urinary bladder, the capsaicin-gated ion channel TRPV1 is expressed both within afferent nerve terminals and within the epithelial cells that line the bladder lumen. To determine the significance of this expression pattern, we analyzed bladder function in mice lacking TRPV1. Compared with wild-type littermates, trpv1^−/− mice had a higher frequency of low-amplitude, non-voiding bladder contractions. This alteration was accompanied by reductions in both spinal cord signaling and reflex voiding during bladder filling (under anesthesia). In vitro, stretch-evoked ATP release and membrane capacitance changes were diminished in bladders excised from trpv1^−/− mice, as was hypoosmolality-evoked ATP release from cultured trpv1^−/− urothelial cells. These findings indicate that TRPV1 participates in normal bladder function and is essential for normal mechanically evoked purinergic signaling by the urothelium.