Cannabis use by adolescents is a public health problem because it can cause cognitive impairment and educational deterioration. The objective of this study was to assess the prevalence and correlates of cognitive impairment among male adolescents with cannabis use in comparison with a control group. This is a case-control study that included 1682 adolescents who just finished their secondary school. A drug screen was made for all participants. Cognitive assessment using Montreal Cognitive Assessment (MoCA) scale was carried out for adolescents with positive urine screen for cannabis and a control group of adolescents with negative urine screen for drugs. The prevalence of cannabis use among adolescents was 2.14%. About one third of the cases started to use cannabis before the age of 15 years. Fifty-six percent used cannabis frequently (>4 times/wk). Adolescents with cannabis use were more likely to have cognitive impairment based on MoCA than controls (78% vs. 44%, P=0.004). Cases were more likely to have impairment in naming, abstraction, orientation, and total MoCA score than controls. Adolescents who started cannabis use early (below 15 y) had impairment in visuospatial/executive, attention, language, abstraction, delayed recall, and total MoCA score compared with those who started late (above 15 y). In addition, adolescents who use cannabis frequently had impairment in all cognitive domains except naming compared with those who used it occasionally. To conclude, the current study found that adolescents with cannabis use were more likely to have cognitive impairment than controls and this impairment was associated with age of onset and frequency of cannabis use.