The presence of osteophytes compressing the sympathetic structures in the thorax was found in 655 (65.5%) of 1,000 cadavers. In 60.4% of the affected cases, the compression was on the right side, and in 36.9% it was bilateral, although the right side was more severely affected. In 2%, the compression was on the left only. The highest frequency of compression was at the T8-10 level, the right greater splanchnic nerve being the structure most frequently involved. The sympathetic trunk itself (ganglia and cord) was affected only by osteophytes of vertebrae at the lowest thoracic levels; however, bony excrescences due to costovertebral joint arthritis were frequently found impinging on the sympathetic trunk and its rami communicantes at similar frequencies on both sides. The factors governing the characteristic compression of the sympathetic structures in the thorax are the typical development of the osteophytes and the special relations of the sympathetic structures to the vertebral column at the various levels. It is proposed that these observations are useful in understanding certain observed clinical conditions and act an anatomic baseline for research in the future.