Prolonged hill walking/hiking activity places significant physical demands on participants that are influenced by the environment. Cold conditions combined with inappropriate clothing presents a serious challenge to body temperature regulation during hill walking/hiking. Advances in clothing design have enabled the development of apparel with heating apparatus to purportedly improve thermal insulation and reduce the risk of hypothermia-related events. Such investigations have not been conducted to date however. The aim of this study was to therefore examine the effect of a heated garment on the physiological responses to simulated hill walking in the cold. Four healthy males (mean±SD body mass 80±2kg, age 29±7 years) completed 2 simulated hill walks (5 km/h at 8% incline for 45 min, rest for 10 min and 4 km/h at 0% incline for 45 min; Weller et al., 1997; Ainslie et al., 2002) in 3°C in a randomised and counterbalanced manner. A fan was placed in front of participants to simulate wind. Participants wore a jacket that contained heating elements incorporated into the front and back of the jacket that were switched on (HEATED) or turned off (CONTROL) during the 2 trials. The same clothes under/in addition to the jacket were worn on both visits. Skin (lateral calf, anterior thigh, stomach, sternal, lateral upper arm and scapula) and core (intestinal) temperatures, heart rate (HR; short-range telemetry), Ratings of Perceived Exertion (RPE; 6-20) and upper and lower body thermal comfort ratings (TC; 1-9) were recorded at 5-minute intervals and were analysed using repeated measures ANOVA (main effects of time and condition). HR increased during exercise (P<0.05) and was not different between HEATED and CONTROL trials (96±16 vs. 101±17 beats.min-1, respectively, P>0.05). Lower body skin temperature was not different between HEATED and CONTROL trials (24.4±1.9 vs. 24.1±2.0 °C, respectively, P>0.05) but upper body skin temperature (33.5±0.5 vs. 32.1±0.4 °C, P<0.05) and weighted mean skin temperature were higher during HEATED (30.9±0.8 vs. 29.8±0.8 °C, P<0.05). The increase in core temperature was not different between trials (HEATED; 0.4±0.2 vs. CONTROL; 0.4±0.2 °C, P>0.05). RPE increased during exercise (P<0.05) and was not different between trials (9±1 vs. 9±1 AU, respectively, P>0.05). Lower, upper and whole-body TC decreased in the 2nd half of the protocol (all P<0.05). Lower body TC was not different between trials (HEATED; 4.7±0.4 vs. CONTROL; 4.6±0.5 AU, P>0.05), whereas upper body (5.3±0.3 vs. 4.9±0.4 AU, P<0.05) and whole-body (5.9±0.4 vs. 5.2±0.5 AU, P<0.05) TC were higher during HEATED. These findings indicate that a heated jacket increases upper body skin temperature and upper body thermal comfort, but does not affect lower body skin or core temperatures or heart rate or ratings of perceived exertion during simulated hill walking in the cold.