Cryogenic tissue ablation instruments for treating body tissue include an elongate flexible body with a proximal supply port for coupling with a pressurized coolant a supply lumen in fluid communication with the proximal supply port, and an expandable cryogenic balloon carried on a distal portion of the elongate body. A dispersion member coupled to a distal end portion of the elongate body has an interior lumen in fluid communication with the supply lumen, the dispersion member having one or more coolant dispersion apertures in fluid communication with the balloon interior and sized and located with respect to the balloon wall such that a pressurized flowable coolant in the supply lumen enters the balloon interior as a liquid spray that provides (through rapid evaporation) substantially uniform cooling of an interior wall surface of the balloon.
