In brief Two endurance athletes developed diarrhea and fecal incontinence each time they exercised strenuously. Such gastrointestinal difficulties are usually benign, but physicians determined that the disorders were an unusual presentation of lumbar spondylolisthesis in a runner and of jejunal diverticulosis in a cyclist. The runner's diarrhea and incontinence resolved when she avoided activities that precipitated her symptoms, and the cyclist's condition resolved with oral tetracycline.