Introduction: Dementia is considered as a serious threat for over 65years old population, because of its high prevalence rates. Dementia with a complex and multifaceted nature has negative effects on patients, family members, and their caregivers' psychological health and socioeconomic status. The current qualitative study is designed to investigate the stigma phenomenon to dementia in Iranian population. Methods: This qualitative research was conducted by the descriptive phenomenological method. In order to analyze the data, the Colaizzi's descriptive phenomenological method was used. The target population consisted of all patients with dementia and their family members in neurological clinics of Tehran. We interviewed with patients and one of the main family members until data saturation. Participants included the main family members (spouse and children) of people with dementia (nine women and six men) who were selected by a nonrandom purposeful sampling method. Results: Two main themes emerged from data analysis: dysfunctional beliefs and negative social attitudes. Each main theme integrates the classes and clusters which are constituted by formulated meanings. Conclusion: Dimensions of stigma, such as dysfunctional beliefs and negative social attitudes, in addition to undesirable effects on patients and caregivers lives, is considered as a serious obstacle to effective caring and providing a good quality of life. It can be concluded that, higher levels of awareness, management, and coping with this powerful phenomenon are capable of preventing, rehabilitation, and improving the psychosocial health in elderly population.