There is no prospective study of mild cognitive impairment (MCI) in India. This study aims to determine the prevalence rate of dementia and to prospectively analyze a group of patients with MCI. A door-to-door cross-sectional cluster survey was conducted in Kolkata, India, among those aged >50 years to estimate the prevalence rate of dementia. Then annual assessment of cognitive function using a validated questionnaire battery was undertaken among 21 elderly individuals with memory complaints for 4 consecutive years. A total of 53,907 persons were surveyed. The crude prevalence rates of dementia were 0.62% (95% CI 0.44-0.84) and 1.25% (95% CI 0.87-1.74) among those >50 and >60 years of age, respectively. The weighted prevalence rate among those above 50 years was 0.95% (95% CI 0.68-1.29). Alzheimer's disease was the commonest subtype (55%) followed by vascular dementia (36%). In a prospective study, MCI remained static, converted to dementia or reverted to normalcy. There was also transition from one subtype of MCI to another. A similar outcome of MCI is also noted in Western nations. However, the prevalence rate of dementia in Eastern India remained quite low.