Cortical calcifications, ween on X-ray in the brain of achild suffering from leukaemia, were submitted to morphological and chemical analysis. The morphology was studied by a combination of low teperature ashing and microscanning. The calcification principally affected axons and capillary walls and consisted of spherules amalgamated into hollow cylinders. The results of chemical analysis of the calcified material were compared and structure of both types of calcification were similar, but the Mn concentration washigher in case of Fahr's disease. X-ray diffraction showed that the calcification consisted of amorphous calcium phosphate and acid calcium orthophosphate, most probably precursors of hydroxyapatite..