In briefApproximately 350 female runners in the 1980 Boston Marathon and the Bonne Bell 10-km race answered a questionnaire about running and menstrual history. Most of the women (69.4%) continued to menstruate regularly, 19.3% menstruated at irregular or infrequent intervals, and 3.4% had not menstruated during the previous year. Although there was a statistically significant trend toward fewer menstrual periods in runners with low body weight and high training mileage, less than one fourth of the women had both low weight and high mileage. The authors suggest that physicians seek explanations besides running when evaluating female runners with menstrual irregularity.