Unintended pregnancy disproportionately affects young Australian women. However, contraceptive behaviours associated with unintended pregnancy are unclear.The objective of this article was to examine contraceptive use before unintended conception.Data from 3795 women (aged 18-23 years) who completed the baseline Contraceptive Use, Pregnancy Intention and Decisions (CUPID) study were analysed.The study found that 21.1% of participants reported ever being pregnant, of whom 84.6% indicated 'accidental' pregnancy. Most (73.4%) of these participants reported using contraception at the first unintended pregnancy, with the combined oral contraceptive pill being the most frequently used form (39.1%). Participants who reported unintended pregnancy were older (21.2 years of age ± 1.7) than those who had never been pregnant (20.5 years of age ± 1.7). They were also more likely to be in cohabitating relationships (34.7% versus 26.0%) or engaged/married (20.1% versus 8.4%).Most participants in this study considered their pregnancy to be accidental. The high rate of contraceptive use before becoming pregnant indicates the need to examine better ways to enhance the efficacy of contraceptive use among young Australian women.