Chemotherapeutic treatment for malignant disease may cause infertility secondary to gonadal failure. In-vitro fertilization (IVF) with embryo cryopreservation prior to chemotherapy has been described as a means of preserving future fertility potential. However, the supraphysiological levels of sex steroids that result from ovarian stimulation for IVF may, at least theoretically, stimulate growth of malignant cells in a patient with a hormonally sensitive tumour such as carcinoma of the breast. This report describes a patient with carcinoma of the breast who underwent IVF in the natural cycle prior to embarking on a course of combination chemotherapy. Of three oocytes retrieved, two fertilized and were cryopreserved. This case represents a novel application of IVF with embryo cryopreservation in the natural cycle. Although embryo thawing and transfer have not yet been attempted, the patient has already benefitted psychologically from having the opportunity to assume an element of control over her reproductive future. Should pregnancy occur, this would be the first report of human pregnancy from cryopreserved embryos obtained in a natural cycle.