This article presents a critical analysis of the case-law of the ECtHR with regards to the interpretation of the notion of ‘a person of unsound mind’ under Article 5 § 1(e) of the Convention. According to the Court, only a person who has been reliably diagnosed with a mental disorder and who poses a danger to himself or others can be legally detained as ‘a person of unsound mind’. However, the notion of ‘unsoundness of mind’ is not limited to such mental disorders which are treatable or which deprive the persons affected of their ability to self-control and so in the past the Court applied the said provision of the Convention to, among others, persons diagnosed with personality disorders or paedophilia who commited crimes acting with full criminal responsibility. [---]