Introduction and Aims To assess the demographic profile, use patterns, market characteristics, reasons for first use and self-reported harms associated with use of synthetic cannabinoids in Australia. Design and Methods An online questionnaire was administered to a purposive sample of 316 Australian synthetic cannabinoid users [96% cannabis users, 77% male, median age 27 years, interquartile range (IQR) 2334] who self-reported demographic and drug use characteristics. Results The median duration of synthetic cannabinoid use was 6 months (IQR 210), 35% reported use weekly or more often and 7% reported daily use. Reasons for first use included curiosity (50%), legality (39%), availability (23%), recreational effects (20%), therapeutic effects (9%), non-detection in standard drug screening assays (8%) and to aid the reduction or cessation of cannabis use (5%). Users reported buying a median of 3g (IQR 36) and paying a median of AU$60 (IQR 3790). Most (68%) reported at least one side-effect during their last session of use, including decreased motor co-ordination (39%), fast or irregular heartbeat (33%), dissociation (22%), dizziness (20%), paranoia (18%) and psychosis (4%). 4 respondents reported seeking help. A greater number of side-effects were reported by males, those aged 1825 years, water pipe (bong') users and concurrent alcohol drinkers. Discussion and Conclusions The sample reported first using synthetic cannabinoids due to curiosity, legality, availability, effects, non-detection in drug testing and to reduce their cannabis use. Harms were widely reported yet help-seeking was minimal. Inclusion of questions regarding synthetic cannabinoids in household surveys is warranted. [Barratt MJ, Cakic V, Lenton S. Patterns of synthetic cannabinoid use in Australia. Drug Alcohol Rev 2013; 32: 141-146]