The material comprises 195 cases of osteogenic sarcoma in children and adolescents. The tumours were grouped in accordance with two classifications; gradual classification which incorporates three levels of morphological maturation of sarcoma and structural classification which distinguishes conventional and nonconventional types of sarcoma. In every case histological mapping of the tumour was performed with the aim to establish the percentage of necrosis and postnecrotic resorbtion of the tumorous mass after the initial chemotherapy. The purpose of this study was to establish the correlation of the tumour necrosis with both histopathological classifications. The main conclusion was, that the gradual classification is more accurate for the changes occurring in the tumour tissue after chemotherapy.