A 28-year-old long-distance runner experienced fever, chills, and brown urine 24 hours after a six-mile run. This was accompanied by a large rise in the creatine phosphokinase level and a rise in echovirus 9 titers from 1:16 to greater than 1:256 during a two-week period. A muscle biopsy specimen showed acute rhabdomyolysis, but no viral inclusion particles. Muscle energy metabolism analysis demonstrated no abnormalities. The patient was treated with forced saline diuresis, and he maintained normal renal function. He subsequently returned to long-distance running and has remained well for one year after the episode. This represents the first reported case, to our knowledge, of acute rhabdomyolysis associated with an echovirus 9 infection.