Dementia implies a loss of the brain functions, usually having a progressive and irreversible character, a pathological modification occurring at the brain level, and causing neuronal injury and loss. In the last few years, the results of several long term monitoring studies indicated the fact that a series of changeable risk factors (vascular risk factors and risk factors associated to lifestyle), together with their well-known connection with the cardiovascular diseases, are also important for the onset of dementia. The objective of the study was to evaluate the comorbidity between Alzheimer’s dementia, vascular dementia, mixed dementia with diabetes and obesity and to establish the causal relationship between diabetes, as risk factor, and dementia. The results show that the risk factors are: old age, low instruction level, obesity, hypercholesterolemia, major episode in clinical records, especially associated with craniocerebral trauma; in the case of patients with vascular dementia, obesity, especially in men, cerebrovascular and cardiovascular disease, cerebral vascular accident and, to a smaller extent, diabetes mellitus.