Malignization of diaphyseal aclasis

8 secondary chondrosarcomas in 7 patients with diaphyseal aclasia are reported. Effective diagnostic imaging is a key to early operative removal of the tumours. Angiography proved to be highly useful in tracing the malignant character and true extension of the lesion. Also skeletal nuclear investigations support the diagnosis. The necessity of regular checkups of all patients suffering from diaphyseal aclasia is stressed.