In brief: The authors opened a runners' clinic to evaluate and treat problems of runners who run 20 miles a week or more. Of 161 patients treated during the first year, 49 had disorders of one or both knees. Fifteen complained of patellofemoral pain, 14 of iliotibial band pain, and 20 of medial or lateral pain. Extremity malalignment and other preexisting problems were involved in several cases. Treatment was mainly conservative, with some restriction or change in activity. One way to help prevent such knee problems is to limit sudden changes in workout intensity.