The current study documents the changing rates of cannabis use, misuse and cannabis-related social harms among Australian adolescents as they grow into young adulthood. It utilised data from a longitudinal study of young people at ages 15, 16, 17, and 19. The rates of cannabis use were found to increase as participants aged; past year use increased from 7.5% at age 15 to 29.8% at age 19. Further, at ages 17 and 19, cannabis use was more prevalent among males than females. Among those who reported cannabis use, the rates of cannabis-related harms were low to moderate, and did not increase with age in the same manner as rates of cannabis use. The most prevalent self-reported cannabis-related harm was anxiety/depression; affecting between 20-30% of the cannabis users at each age. These findings may assist in understanding the extent of cannabis-related problems among youth, and in planning relevant services. (Contains 4 tables and 2 figures.)