The paper refers to the neurochemical theories explaining the etiopathogenesis of obsessivecompulsive disorder, and among them those that focus on the neurotransmission system. The existence of dysfunctions in serotonin, dopaminergic, noradrenergic systems, and most recently, cholecystokinin were reported by different authors, but without specifying whether these disorders are the cause or the effect of the installation of mental disorders. It refers to the common biological spectrum between the obsessive-compulsive disorder and other psychiatric disorders such as pathological gambling, paraphilias, dysmorphophobias, trichotillomania, hypochondria, somatization disorder, Gilles de la Tourette syndrome, autism, Asperger syndrome, kleptomania, bulimia, anorexia nervosa. It is stated that the hypothesis of the neurotransmitter system malfunction revealed some peculiarities in the therapeutic treatment of obsessive-compulsive disorder. So far no existing theory met the necessary evidence to explain the neurobiological psychiatric disorder. It can be assumed only the substantial role played by the serotonin neurotransmission in the genesis of the obsessive-compulsive disorder.