Cyclophosphamide treatment can cause premature ovarian failure. This pilot study evaluates the protective effect of the gonadotrophin releasing hormone (GnRH) antagonist, cetrorelix, on ovarian function, when used during cyclophosphamide chemotherapy in women aged 18–35. Primary outcomes measured were serum follicle stimulating hormone (FSH) and inhibin prior to and at 6 and 12 months after chemotherapy. Secondary outcomes were hormonal evidence of a suppressive effect and the side effect profile.