Old age is a qualitative state during which depression frequently occurs. This illness presents particular features which should be considered in the course of both normal ageing and senility. Viewed as an existential crisis, ageing may be considered as a depression promoting factor. Rich in depression promoting factors, this period of life is a sequence of crises which result in reorganizations heavily dependent on the adaptive capabilities of the aged person. During ageing, depression exhibits particular features that one should be able to recognize and distinguish from the consequences of deficits that are the normal adjuncts of the ageing process. The same is true of alterations occurring in the cognitive sphere and which might result from demential alteration. During ageing, depression should be identified among the other decompensation patterns occurring in the aged patient by viewing the situation in terms of overhelmed mechanisms. Depression exhibits a pattern whereby it relates closely with the risk of dementia. Therapeutic management should take into account such a perspective, that one might call transnosographic, when considering the depressiveness of aged patients as a high-risk situation requiring long-term follow-up of their biological, psychodynamic, social and cognitive functions.