In order to examine thermoregulatory response to creatine (CR) supplementation, competitive male cyclists and triathletes (n = 7, O2max = 50.6 ± 0.8 ml·kg−1·min−1) completed three 1-hour hyperthermic (ambient temperature = 38.7 ± 1.0°C, relative humidity = 33 ± 4%) exercise sessions at 181 ± 12 W (50% of Wmax, approximately 66% of O2max). Subjects completed a baseline (BL) session, then 2 sessions following 5 days of CR (20 g·d−1) and placebo (PL, 20 g·d−1) administered in a double-blind counterbalanced crossover manner with ≥28-day washout. Pre-exercise BL, CR, and PL body mass were unchanged, with similar decreases in postexercise mass among the three conditions. Tympanic temperature, heart rate, systolic blood pressure, perceived exertion, and lactate, cortisol, and aldosterone concentrations increased similarly during BL, CR, and PL exercise. A greater (p < 0.013) estimated decrease in plasma volume occurred following BL (−16.5 ± 2.0%) and PL (−17.6 ± 1.7%) exercise compared to CR (−13.5 ± 2.1%). Creatine supplementation reduces plasma volume loss during 1 hour of hyperthermic exercise but does not appear to otherwise change thermoregulatory response to hyperthermic exercise.