Background The average age of participants in mass-participation community-based endurance running events is slowly increasing. The prevalence of long-term medical conditions in marathon participants can inform medical planning for such events.

Objective To describe the prevalence of long-term medical conditions (LTMC), including cardiovascular disease (CVD) risk factors, in participants of mass-participation community-based marathon events.

Design Observational questionnaire-based study.

Setting Two large UK city mass-participation marathon events.

Patients (or Participants) Entry to both events was open to novice runners, with no qualifying time for general entry. All registered participants were invited to complete an online questionnaire in the week preceding the event. 11809 runners completed the survey.

Interventions (or Assessment of Risk Factors) Demographics including age, gender, medical history, medication and smoking.

Results The average age of respondents was 40.9y (range 18–83y) and 54.1% were male. 42.3% of respondents had never completed a marathon event before. 1995 (16.9%) of all respondents had a LTMC. Most (95.7%) were aware of their condition prior to entering but only 47.0% had seen a doctor about their health with respect to the event. Respiratory conditions such as asthma were the most common LTMC (36.2%). 363 (18.2%) of LTMCs were related to a cardiovascular cause (hypertension, hypercholesterolaemia, previous myocardial infarction or angina, previous stroke/TIA or Type 2 diabetes mellitus). 35.1% were current or ex-smokers. 72.0% of those with aLTMC were taking prescribed medication (compared to 11.2% of those without a LTMC).

Conclusions In this study on runners in mass-participation community-based marathon events, approximately 1 in 6 respondents had a long-term medical condition. Further study will improve our ability to counsel individuals who wish to participate in endurance running events and help event organisers and medical teams to plan for reasonably anticipated medical conditions.