One hundred fifty-nine patients were referred to the authors for evaluation of chronic exertional leg pain from 1978 to 1987. The records of 131 patients were complete and available for retrospective review. Forty-five patients were diagnosed as having a chronic compartment syndrome (CCS) and seventy-five patients had the syndrome ruled out by intramuscular pressure recordings. The only significant difference found between the two groups on history and physical examination was a 45.9% incidence of muscle herniae in the patients with CCS, compared to a 12.9% incidence in those without the syndrome. One-third of the patients with the syndrome and over one-half of those without it reported persistent, moderate to severe pain at 6 month to 9 year followup. Modified, objective criteria were developed for the diagnosis of CCS. The criteria were based upon the intramuscular pressures recorded with the slit catheter before and after exercise in 210 muscle compartments without CCS. In the presence of appropriate clinical findings, we consider one or more of the following intramuscular pressure criteria to be diagnostic of chronic compartment syndrome of the leg: 1) a preexercise pressure greater than or equal to 15 mm Hg, 2) a 1 minute postexercise pressure of greater than or equal to 30 mm Hg, or 3) a 5 minute postexercise pressure greater than or equal to 20 mm Hg.