The article discusses the issue of an anonymous letter as a basis for initiating the preparatory proceedings. The author presents the issue of anonymous letter, including in particular its definitions, public perception and the reasons why their authors do not want to reveal their identity. It is being stated that, as a stand-alone basis, an anonymous letter cannot constitute a notice of a committed crime. However, an anonymous letter may contain information which, if the relevant authorities give their consent, will give rise to an investigation.