The aim of this study was to examine trends in cannabis use among Spanish students from 2006 to 2018 by sex, age, and sex and age combined. Data showed a global decrease both in a lifetime and frequent cannabis use between 2006 and 2018 but four-year comparisons revealed more variability within the specific sex-age groups. No change was found in lifetime use between 2014 and 2018 for all groups. The results emphasize the need for ongoing monitoring of trends in cannabis use and the importance of implementing preventive measures to avoid a change in tendency and to work with high-risk groups, especially 17-18-old boys.