Context: Cancer treatment may impair fertility in patients so fertility preservation (FP) methods were introduced to prevent it. Knowledge and awareness about FP is an emerging aspect of quality of life for them. However, decision making and use of FP among cancer patients and their families depends on the knowledge and attitudes of the patients and the physicians together. Objective: To determine knowledge and attitude of cancer patients about FP. Methods: Patient (s): 397 cancer patients were recruited via convenience sampling of patients undergoing cancer treatment and parents of minors referred to two large referral hospitals in Tehran, Iran, from December 2015 to January 2016. Main outcome: Knowledge and attitude of cancer patients about FP. Measures: A 25-item self-administered questionnaire was developed to measure self-perception. Question types included yes/no, multiple choice and 4-point Likert scale for Knowledge and attitude assessment. Results: Male responders reported mean knowledge of ovarian tissue cryopreservation score of 1.97(CI95%: 1.8-2.14), oocyte cryopreservation score of 1.97 (CI95%: 1.83-2.14), ovarian transposition score of 1.97 (CI95%: CI95%: 1.8-2.14) and Gonadotropin-releasing hormone (GnRH) score of 1.99 (CI95%: CI95%: 1.89-2.09), higher than female participants (P=0.015, P=0.002, P=0.021 and P=0.044, respectively). Patients under 18 years showed mean knowledge of IVF with embryo cryopreservation scores of 1.96(CI95%: 1.77-2.15) and sperm cryopreservation scores of 1.97(CI95%:1.81-2.13), respectively; higher than patients over 18 years; (P=0.036 and P=0.019, respectively). Male participants were more positive attitude than female participants toward disappointment of the treatment process as a main reason for failure of FP use [2.04(CI95%:0.78-3.3) vs. 2.36 (CI95%:1.08-3.64), (P=0.040)]. Patients over 18 years more agreed with risk of recurrent [2.58(CI95%:1.29-3.87) vs. 2.09(CI95%:0.83-3.35), P=0.002] as a main reason for failure of FP use. However, Patients under 18 years were supportive to unavailability of FP [3.44(CI95%: 2.39-4.49) vs. 3.00(CI95%: 1.81-4.19), P=0.003] and lack of information about FP [3.75(CI95%: 3.07-4.43) vs. 3.17(CI95%: 2.01-4.33), P< 0.001]. Conclusion: This is the first survey that focuses on cancer patients’ knowledge and attitude of all existing FP services. Knowledge of cancer patients about FP was very low bringing up the necessity of informing all cancer patients about FP methods.