Nitrosourea is an anticancer agent that can cross the blood-brain barrier. Nitrosourea derrivatives represent one of the most active classes of agents in the treatment of high-grade gliomas and glioblastoma. Nitrosoureas are alkylating agents with a long history in cancer treatment. Their mechanism of action is represented by the alkylation of DNA strands, which results in DNA damage and cellular death. In particular, the chemical decomposition in aqueous solutions determines the formation of two reactive intermediates: a chloroethyldiazohydroxide and an isocyanate group. The former further decomposes into a chloroethyl carbonium ion that forms adducts and crosslinks to DNA, while isocyanates deplete glutathione, inhibit DNA repair, and alter maturation of RNA. All these chemical interactions result in cellular damage and death.