Boldt, P, Knechtle, B, Nikolaidis, P, Lechleitner, C, Wirnitzer, G, Leitzmann, C, and Wirnitzer, K. Sex differences in the health status of endurance runners: results from the NURMI study (step 2). J Strength Cond Res 33(7): 1929-1940, 2019-Optimized endurance performance is closely linked to a good health status (HS), which is crucially affected by sex. Therefore, the purpose of this study was to investigate sex differences in the HS of endurance runners of different distances. A total of 281 female and male recreational runners completed an online survey. Health status included body mass, smoking habits, felt stress, chronic diseases, allergies, intolerances, medication intake, supplement intake, health-related food choice, enhancement substance use, and health care utilization. Data analysis was performed using the independent t-test and chi-squared test with Cohen's d and Cramer's phi (φ) to evaluate the magnitude of the differences and associations. There were 159 female and 122 male participants, with 173 runners meeting the inclusion criteria, among them 103 half-marathoners, and 70 marathoners and ultramarathoners, of which one hundred eight 10-km runners were defined as the control group. Statistical significance (p < 0.05) was determined for the following findings: there was a higher prevalence of hypothyroidism in women; the use of thyroid medication and the intake of hormones and supplements prescribed by a doctor were more common in women; men reported more often a decrease in body mass due to running training, and women reported more often choosing food to obtain phytochemicals. There was no statistically significant association (p > 0.05) between sex and body mass change because of a change in diet, smoking habits, felt stress, chronic diseases except hypothyroidism, allergies, food intolerances, intake of antihypertensives and cholesterol-lowering medication, intake of performance-enhancing substances, or health care utilization. Both female and male runners had a good HS with no difference between sexes. Based on the findings of this study, monitoring thyroid parameters and vitamin D levels is required in female athletes, whereas adequate body mass control strategies are needed for their male counterparts.