The prognosis of malignant ovarian tumours depends upon the stage at the onset of treatment when the histology is similar and in tumours of the same stage upon the histologic type of tumour. Ovarian cancers were histologically divided into 7 groups. The diagnosis in our series allowed to consider the following groups: Germinal cell tumours (group 1), tumours arising from isolated epithelial rests (group 2), tumours of follicular cell origin (group 3), tumours of the covering epithelium (group 4), and genetically indeterminate tumours (group 6). The stage T1 at the onset of treatment was most frequently diagnosed in tumours arising from follicular cells (61%). Tumours arising from the covering epithelium or genetically indeterminate tumours showed stage T1 in 15 or 16%. Secondary tumour at the onset of therapy was found in increasing frequency from group 1 to group 6. The survival rate decreases from group 1 to group 6. The worst prognosis show patients with genetically indeterminate tumours, followed by patients with malignant tumours of the covering epithelium. The best survival chance have patients with tumours of the germinal epithelium. It is therefore important to plan the post-operative treatment not only according to the stage of tumour but also according to the microscopic findings.