We report a case of a 10-year-old girl with a tumour of the right temporoparietal region of the brain. The tumour consisted of three morphologically distinct portions: a well-differentiated one containing a mixture of a ganglioglioma with adipocytic-like cells and focal chondroid metaplasia, a separate island with neurocytic differentiation, and the malignant one, which exhibited an organoid pattern (trabecular and festooned) of primitive neuroectodemal tumour (PNET). We hypothesize that the latter component originated from the multicomponental glioneuronal tumour with mesenchymal differentiation and thus that lesion constituted an unusual example of malignant transformation of low-grade glioneuronal neoplasm.