Background Data on the prevalence of acute illness in the period prior to a distance running race are limited. Currently, the presence of systemic symptoms (failed ‘neck check’) is used to advise athletes on participation.

Aim To determine (1) the period prevalence of pre-race acute illness symptoms before a distance running event, (2) if symptomatic runners receiving educational material on acute illness did not start (DNS) the race and (3) if symptomatic runners who chose to start the race, did not finish (DNF) the race.

Methods 7031 runners completed an online pre-race acute illness questionnaire in the 3–5 day period prior to a race. Symptomatic runners received educational information on exercise and acute illness. Runners were followed prospectively to determine DNS and DNF risk.

Results 1338 runners (19.0%) reporting symptoms (7.5% reporting systemic symptoms—failed ‘neck check’) and receiving educational information had a higher DNS frequency (11.0%) compared to controls (6.6%)(p=0.0002). Symptomatic runners who started the race had a higher DNF frequency (2.1%) compared to controls (1.3%) (p=0.0346), particularly runners with systemic symptoms (2.4%; RR=1.90).

Conclusions In summary, 19% (1 in 5) runners reported pre-race acute illness symptoms, with 7.5% (1 in 13) reporting systemic symptoms. Although runner education reduced the percentage symptomatic race starters, the majority of them still chose to race, resulting in a two times higher risk of not finishing in those with systemic symptoms. Pre-race acute illness symptoms are common; an educational intervention affects an athlete's decision to compete yet most symptomatic runners still competed, and systemic symptoms negatively affect performance, with possible health implications.