The aetiology of pain in the lower leg during exercise has been studied in 110 athletes by monitoring intracompartmental pressure during exercise and by technetium bone scans. Patients were assigned to three diagnostic groups: chronic compartment syndrome, medial tibial syndrome and those with non-specific findings. Our results indicate that subcutaneous fasciotomy of the affected compartment(s) is the treatment of choice for chronic compartment syndrome. The treatment of patients with medial tibial syndrome, either by operation or conservatively, has been unsuccessful; non-specific symptoms have been treated conservatively with success.