Marijuana is one of the most used psychoactive substances by young people, this substance can cause different clinical conditions including neuropsychological alterations. This article presents an investigation which has analyzed the influence of marijuana use on neuropsychological functions of attention, memory and executive functions, in a group of 16 young people (8 men and 8 women) who maintain regular-recreational and intensive-habitual consume of the above mentioned substance (Mage = 23.38; SD = 1.78), when compared with a group of 16 young people (8 men and 8 women) who do not consume marijuana (Mage = 22.25; SD = 1.92). The results indicate that regular-recreational and intensive-habitual consumption of marijuana in young people causes alterations in the functions of selective and sustained attention, short-term and long-term memory, operative memory, planning, mental flexibility and inhibitory control. A discussion of the results is made based on previous research, emphasizing mainly on the harmful effects that the marijuana could cause in the cognitive functions that were studied, and that generally this effects are not recognized or they are minimized by young people who use marijuana.