Dementia is a syndrome of global and progressive deterioration of acquired cognitive skills with preserved consciousness, where memory, learning, abstract thinking, orientation and understanding of visual-spatial relationships are particularly affected. As the progressive dementias for now cannot be healed or significantly halted, given the aging population and increasing life expectance, in the near future dementia will become one of the leading medical, social and economic global problems. Increasing number of studies suggest the potential role of the serotonergic system, particularly 5-HT6 receptors, in various cognitive functions such as learning and memory. The associations of individual polymorphisms in the gene coding for 5-HT6 receptor with Alzheimer's disease have been found, although the results are controversial. The aim of this study was to determine the possible association of polymorphism C267T (rs1805054) in the HTR6 gene, coding for the serotonin 5-HT6 receptor, with the development of progressive dementia. The results of our study have not suggested the association of rs1805054 polymorphism in the HTR6 gene with the development of dementia in patients with mild cognitive impairment, Alzheimer's disease and other types of dementia such as vascular dementia, frontotemporal dementia and dementia with Lewy bodies. Further extensive studies including different populations, different types of dementia and higher number of participants are needed in order to elucidate the role of serotonin 5-HT6 receptor and HTR6 gene in the pathogenesis of dementia.