To explore knowledge about the effects on fertility of age, obesity, smoking, and timing of intercourse among Australians of reproductive age. DESIGN: Telephone survey of a representative sample of Australians. SETTING: Not applicable. PATIENT(S): Australians aged 18 to 45 years who wish to have a child or another child now or in the future. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Knowledge about the effect on fertility of age, obesity, smoking, and timing of intercourse. RESULT(S): A total of 462 interviews were conducted. The majority of respondents underestimated, by about 10 years, the age at which male and female fertility starts to decline. Only one in four correctly identified that female fertility starts to decline before age 35, and one in three identified that male fertility starts to decline before age 45. Most (59 ) were aware that female obesity and smoking affect fertility, but fewer recognized that male obesity (30 ) and smoking (36 ) also influence fertility. Almost 40 of respondents had inadequate knowledge of when in the menstrual cycle a woman is most likely to conceive. CONCLUSION(S): Considerable knowledge gaps about modifiable factors that affect fertility were identified. These are targeted in a national education campaign to promote awareness of factors that influence fertility. Copyright ? 2013 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.