Intramuscular pressure was recorded in 80 patients suspected of suffering from chronic anterior compartment syndrome in the lower leg; the diagnosis was verified in 22 of these patients. The history and clinical findings of the chronic compartment syndrome patients were compared with those of the 58 patients without the syndrome. Pain induced only by athletic activity and only in the anterior lower leg forcing the patient to interrupt running indicated chronic compartment syndrome. The history and clinical findings alone were found to be insufficient to establish the diagnosis. In relation to generally accepted pressure parameters at rest, the muscle relaxation pressure during exercise was found to be a reliable parameter for diagnosing chronic compartment syndrome, whereas mean muscle pressure and muscle contraction pressure were found to be unreliable.