Cryopreservation of ovarian tissue is currently practiced in an attempt to preserve fertility before commencing potentially sterilizing chemotherapy. Clinical and laboratory guidelines are needed to standardize the procedure. Over the last 10 years ovarian tissue was stored in female patients with hematologic malignancies. Patients' records and consultation charts were evaluated, surgical and laboratory reports were revised and ovarian histology was investigated. Fifty-six patients with hematologic malignancies (age 24 +/- 5.5) had cryopreserved ovarian tissue. Thirty-three patients had Hodgkin's disease, 14 non-Hodgkin's lymphoma, 6 acute leukemia, and 3 chronic myelocytic leukemia. Harvesting of ovarian tissue was also performed following previous exposure to chemotherapy (33 patients), 13 of them shortly after the chemotherapy. Partial oophorectomy was the preferred surgical procedure. Fertility was restored with ovarian tissue transplantation in a sterilized patient and following fertility treatment in a patient with very low ovarian reserve. We recommend that indications and timing of ovarian tissue banking should be individualized. Patients previously exposed to chemotherapy can consider ovarian tissue freezing. The extent of tissue removed should take into account the large number of follicles lost and the risk of future sterilization. Tissue handling should enable further investigation of primordial follicles and identification of cancer cells.