In brief: This report examines the type and frequency of self-reported injuries that occurred at the Chicago Distance Classic, a 20km race held each year in July. Questionnaires were sent to the nearly 5,000 entrants. The runners were asked about their medical history and if they had suffered injuries or illnesses from the race. Most entrants had been running two to five years. More than half stretched regularly before and after running. The knee was most often injured (10%), and the foot was second. Most orthopedic, knee, and foot injuries occurred to beginners, and most entrants were between ages 31 and 40. Many of the entrants said they were affected by the heat; 31 said they suffered severely from the heat.