This article analyzes the validity terms of property disposal contracts on condition of lifelong maintenance and shows some classifications of validity terms. With regard to the terms mentioned, there is no controversy, either in doctrine or in law, on the fact that the contract represents the common will of at least two persons to constitute, modify or extinguish the legal relations between them. However we should point out that the document which shows the will of the parties is only a manifestation form of such will. The lack of document, even if the written form is required by law, is not equivalent to the absence of the contract, but only attracts legal consequences. Usually, such consequences are the prohibition of testimony for proof, the unenforceability against third parties or, where this effect is expressly provided by law, the breach of written form entails the nullity of the contract.