A calcified cataractous lens from a 12 year old boy suffering from chronic uveitis was analysed using a microradiographic technique, X-ray crystallography and transmission electron microscopy. A 0.2 mm thick shell of calcified tissue was found in the subcapsular cortex. The mineral consisted of well-crystallized hydroxyapatite with a random orientation of the crystals. The underlying cortex consisted of a fibrous matrix containing collagen fibers. In the matrix, single or groups of epitheloid cells and fibroblast-like cells were found. Membrane-enclosed vesicles were found scattered in the matrix. The content of these vesicles had a wide range of electron density. A cell-induced mechanism for calcification is suggested.