Neurodegenerative and neuropsychiatric disorders are leading causes of disease burden in middle-aged and older adults. We aimed to quantified and estimated the temporal and spatial characteristics of individual and concurrent burden of dementia with eight mental disorders worldwide. Our findings revealed that although a trend of decreased prevalence and incidence of dementia was observed in most regions over the past 31 years, dementia demonstrated greater comorbidity burden of neurodevelopmental disorders (especially attention-deficit/hyperactivity disorder and idiopathic developmental intellectual disability) in Middle East and North Africa. In high-SDI areas such as Western Europe, and high-income north America countries, it was more linked to mental disorders including anxiety disorders, eating disorders, and schizophrenia. In addition, neurodevelopmental disorders have been highly comorbid with both early- and late-onset of dementia. Our findings underscore the urgent need for proactive, integrated, and life-course health management strategies to achieve precision prevention and control of dementia, mental disorders and their comorbidities.