Purpose: "Ice-mile" swimming presents significant physiological challenges and potential safety issues, but few data are available. This study examined deep body temperature (BT), respiratory rate (RR), and swim performance in 2 swimmers completing an ice-mile swim of 1 mile (1600 m) in water less than 5 degrees C. Methods: Two male cold-water-habituated swimmers completed a 1-mile lake swim in 3.9 degrees C water. For comparative purposes, they completed an indoor 1-mile swim in 28.1 degrees C water. The Equivital physiological monitoring system was used to record BT and RR before, during, and after each swim. Total time to complete the swims and 400-m splits were recorded. Results: One swimmer became hypothermic after 27 min while swimming, reaching BT of 33.7 degrees C at swim's end. On exiting the water the swimmers experienced large BT after-drops of -3.6 degrees C and -2.4 degrees C, reaching low points of 33.2 degrees C and 31.3 degrees C 38 and 23 min postswim, respectively. Respiratory rate and swim pace decreased over the course of the ice-mile swim for both swimmers. Swim pace for 1 swimmer declined sharply in the final 400-m lap of the ice mile when he was hypothermic. Both swimmers remained hypothermic 60 min postswim (34.2 degrees C and 33.4 degrees C). Conclusions: Ice-mile swimmers may become hypothermic while swimming, and the postswim BT after drop may expose them to dangerous levels of hypothermia. Pace and RR should be monitored as proxies for a swimmer's physiological state. Postswim recovery should also be monitored for hypothermia for at least 1 h.