['Exertional hyponatremia ((Na) < 135 mmol x L(-1)) is a potentially serious condition associated with endurance sports. It has been postulated that nonsteroidal antiinflammatory drug (NSAID) use may be a risk factor. This observational cohort study aimed to determine whether NSAID use is a risk factor for exertional hyponatremia and altered renal function during endurance exercise.', 'A total of 330 athletes in the 2004 New Zealand Ironman triathlon (3.8-km swim, 180-km cycle, and 42.2-km run) were weighed before and after the race. A blood sample was drawn for measurement of plasma sodium (Na), potassium (K), urea (urea), and creatinine (creatinine) concentrations postrace.', 'The incidence of NSAID use was 30%, whereas the overall incidence of hyponatremia was 1.8%. NSAID use was related to the incidence of hyponatremia (P = 0.0002). The NSAID group had lower plasma Na (P = 0.02) and higher plasma K (P = 0.002), urea (P = 0.05), and creatinine (P = 0.01). Lower Na was also significantly related to female gender, lower prerace body weight, younger age and a smaller weight loss during the race. Race times were not associated with plasma Na; however, faster triathletes lost more weight. Estimated fluid intake was not different in the NSAID group, but heavier triathletes reported greater fluid intakes.'] Does nSAID use increase the risk of developing hyponatremia during an Ironman triathlon?