A 24-year-old man presented with severe low-back pain and paraspinal muscle spasm after exertion. Elevation in temperature, white blood cell count, serum muscle enzymes, and urine myoglobin, as well as computer tomographic evidence of paraspinal muscle edema and necrosis, were present. No etiology could be documented, and the possibility of an acute exertional compartment syndrome was entertained. Subsequently, cadaveric dis-sections indicated that the erector spinae muscles are contained within a well-developed fascial sheath. Continuous slit catheter pressure measurements within this compartment in eight healthy male subjects were subsequently carried out. These indicated a physiologic behavior similar to other known compartments for which compartment syndromes have been described. Variation in intracompartmental pressure occurred as a function of body posture, erector spinae isometric contraction, and active intra-abdominal pressurization. We suggest this patient had a paraspinal compartment syndrome and have described pressure characteristics of this compartment in normal men.