Aims: The current burden of cannabis-related presentations to emergency health services is largely unknown. This paper presents data collected over a 13-year period in metropolitan Melbourne, Australia as part of the Ambo Project, a unique surveillance system that analyses and codes paramedic records for drug-related trends and harms. Methods: Cannabis-related ambulance attendances involving 15-59 year olds in metropolitan Melbourne were analysed retrospectively from 2000 to 2013 (. n=. 10,531). Trends and attendance characteristics were compared among cannabis only (CO)-, cannabis and alcohol (CA)- and cannabis with polydrug use (CP)-related attendances. Changes in alcohol and drug involvements in cannabis-related attendances were explored. Results: Rates of cannabis-related ambulance attendances increased significantly over the study period. Increasing rate of attendances per 100,000 population per year changed from 0.6 (2000-2010) to 5.5 (2010-2013). This sharp change was driven by CO- and CP-related attendances (rate of CA-related attendance increased steadily). The highest increasing rate (15.6) was for CO-related attendances among 15-29 years old males (2010-2013). Crystal methamphetamine became the most common illicit co-intoxicant amongst cannabis presentations in 2013. Conclusions: Relative to the total drug-related burden on ambulance services, cannabis-related presentations appear to be a small but significant and increasing problem. Significant changes in trends across other drug involvement and demographic subgroups suggest a possible shift in the cannabis using population and/or a change in using behaviours. Public health strategies should raise awareness of the increased risk posed by cannabis polydrug use and high attendance subpopulations should be determined.