The use of botulinum toxin for the treatment of wrinkles has become very popular in recent years. The botulinum toxin is produced by the Clostridium botulinum bacterium and causes muscle relaxation by inhibiting a chemical substance called Acetylcholine, in the junction between nerve and muscle (neuromuscular plate). It has been used since the 80s for the treatment of neurological and ophthalmic diseases with uncontrolled or excessive muscle contraction. The use of the botulinum toxin in cosmetic began in the 90s, promoting the improvement of expression wrinkles by relaxing specific muscle. It is a safe procedure, since the dose required to cause toxic effects needs to be a thousand times higher than that customarily used in a cosmetic procedure. The action of the toxin is local, causing muscle paralysis, which remains from 2 to 6 months. After this period, the muscle is able to form new plates (neurogenesis), returning to its regular contraction. The action of the botulinum toxin begins 48 hours after the procedure, reaching the maximum result within 15 days. The muscle reacts with relaxation, with no change in skin sensitivity. The application should be avoided in places where the muscles have physiological functions, such as in the mouth area. The botulinum toxin may and should only be injected by expert doctors, i.e., professionals who know both the anatomy of the area and the complete features of the substance used. The doctor should indicate the places for the application, in which the cost/benefit ratio will be positive. The application of the botulinum toxin should be made in a special room, with appropriate accommodations for the expert and patient, with asepsis of instruments and clothing. Moreover, the environment should be quiet and suitable for the concentration required by the procedure. The procedure is slightly painful and it may leave small hematomas that remain for 5 to 10 days. The expression wrinkles may disappear completely for about 6 months. It is not advisable to repeat the application before 2 months. The muscle will always contract again, with no permanent sequels. The botulinum toxin is, therefore, safe and effective for the treatment of expression wrinkles, provided it is diluted and applied correctly. The application of the botulinum toxin should observe the common sense and, therefore, early age, exaggerated amount and successive applications should be avoided. Reapplication may be performed every 6 months.