A prospective study of 40 consecutive classic primary osteosarcomas employing tomography, angiography, radio-scanning, tetracycline labelling, macroscopic and microscopic study revealed that in 10 (25%) "skip" metastases were found. In 8 the "skips" were completely unsuspected prior to computation. It is evident that patients with "skips" are more prone to local recurrence and have a worse prognosis following amputation than those without such satellite lesions. Through-bone amputation entails a considered risk of leaving micro-foci of tumor; proximal disarticulation does not obviate the risk of cross joint "skips" when the lesion is in a sub-articular site. What affect such residual foci has upon the effectiveness of adjunct therapy and conversely whether such therapy will permit more conservative surgery by suppressing residual "skips" is an important but unanswered question.