A round of golf lasts approximately 4 h, during which time homeostasis could be challenged through either hypoglycemia or hypohydration. This might result in impaired motor skill or cognitive performance. Given the high cognitive demand of putting and the potential fatiguing effects from prolonged walking, the combination of a caffeine and carbohydrate drink could be beneficial in offsetting hypoglycemia and hypohydration. This study used a laboratory-simulated round of golf to examine the effect of an isotonic carbohydrate and caffeine sports drink on putting performance during a round of golf. After institutional ethics approval, 20 male golfers (mean +/- standard deviation: age 23 +/- 4 years, stature 176.4 +/- 5.6 cm, mass 72.8 +/- 17.4 kg, handicap 15 +/- 4, daily caffeine consumption 157.3 +/- 47.2 mg) consumed either an isotonic sports drink containing caffeine (6.4 g carbohydrate and 16 mg caffeine per 100 mL) or a no-energy, flavour-matched placebo drink in a double-blind, randomized, counter-balanced crossover design . Drinks were consumed preround (5 mL.kg-1 body mass (BM)) and at holes 6 and 12 (2.5 mL.kg-1 BM). Participants therefore consumed 1.6 mg.kg-1 BM of caffeine and 0.64 g.kg-1 BM of carbohydrate throughout the trial. Five and 2 m putting performance were assessed at each hole. Self-rated mood assessments were carried out every third hole. Putting performance over 5 m and 2 m and self-rated scores for alertness and relaxation showed a main effect for drink (p < 0.05). Ratings of mental fatigue and tiredness significantly increased during the round (p < 0.001). In experienced golfers, the consumption of an isotonic carbohydrate sports drink containing caffeine prior to and during a round of golf improved putting performance and increased feelings of alertness.