Objectives: Cold water immersion (CWI) has been widely used for enhancing athlete recovery though its use following an Ironman triathlon has never been examined. The purpose of this paper is to determine the influence of CWI immediately following an Ironman triathlon on markers of muscle damage, inflammation and muscle soreness. Design: Prospective cohort study. Methods: Thirty three (22 male, 11 female), triathletes participating in the Ironman World Championships volunteered to participate (mean ± SD: age = 40 ± 11 years; height = 174.5 ± 9.1 cm; body mass = 70 ± 11.8 kg; percent body fat = 11.4 ± 4.1%, finish time = 11:03.00 ± 01:25.08). Post race, participants were randomly assigned to a 10-min bout of 10 ◦C CWI or no-intervention control group. Data collection occurred pre-intervention (PRE), post-intervention (POST), 16 h (16POST) and 40 h (40POST) following the race. Linear mixed model ANOVA with Bonferroni corrections were performed to examine group by time differences for delayed onset muscle soreness (DOMS), hydration indices, myoglobin, creatine kinase (CK), cortisol, C-reactive protein (CRP), IL-6 and percent body mass loss (%BML). Pearson’s bivariate correlations were used for comparisons with finishing time. Alpha level was set a priori at 0.05. Results: No significant group by time interactions occurred. Significant differences occurred for POST BML (−1.7 ± 0.9 kg) vs. 16POST, and 40POST BML (0.9 ± 1.4, −0.1 ± 1.2 kg, respectively; p < 0.001). Compared to PRE, myoglobin, CRP and CK remained significantly elevated at 40POST. Cortisol returned to PRE values by 16POST and IL-6 returned to PRE values by 40POST. Conclusion:Asingle bout of CWI did not provide any physiological benefit during recovery from a triathlon within 40 h post race. Effect of CWI beyond this time is unknown.