Abstract In this work the study of the disappearance of cocaine in hair is reported. The subject of the study is a woman who stopped the consumption of cocaine after a period of drug abuse of over 1 year. Hair samples were collected over a period of 10 months. During this time the absence of cocaine intake was monitored by the toxicological analysis of urine, performed every 2 days. After decontamination with methanol, the hair sample, cut in two segments (0–1.5 and 1.5–3 cm from the hair root) was added with cocaine-D 3 (internal standard), hydrolyzed and extracted with chloroform/isopropanol (9:1). The extract was evaporated to dryness, reconstituted in 25 μl of ethyl acetate and analyzed by GC–MS in SIM mode. The obtained results show that the incorporation of cocaine in hair decreased during the first 3 months after the last consumption and after this period of time no cocaine was found in the hair sections closest to the root.