It has been demonstrated that exercise-induced dehydration (EID) does not impair, and ad libitum drinking optimizes, cycling time-trial (TT) performance. However, the idea that EID≥2% bodyweight (BW) impairs endurance performance is well ingrained. No study has tested the impact of EID upon running TT performance. We compared the effects of thirst-driven (TD) vs. programmed fluid intake (PFI) aimed at maintaining EID-associated BW loss <2% on half-marathon performance. Ten trained distance runners underwent, in a randomized, crossover fashion, two, 21.1km running TTs on a treadmill (30°C, 42% relative humidity) while facing a wind speed matching running speed and drinking water (1) according to thirst sensation (TD) or (2) to maintain BW loss <2% of their pre-exercise BW (PFI), as recommended by the American College of Sports Medicine. Despite that PFI significantly reduced EID from 3.1±0.6 (TD) to 1.3±0.7% BW (PFI), mean rectal temperature from 39.4±0.4 to 39.1±0.3°C, mean body temperature from 38.1±0.4 to 37.7±0.2°C and mean heart rate from 175±9 to 171±8bpm, neither half-marathon time (TD 89.8±7.7; PFI 89.6±7.7min) nor running pace (TD 4.3±0.4; PFI 4.2±0.4min/km) differed significantly between trials. Albeit providing trivial cardiovascular and thermoregulatory advantages, in trained distance runners, PFI (1,380±320mL/h) offers no performance benefits over TD fluid intake (384±180mL/h) during a half-marathon raced under warm conditions.