Abstract: The invention relates to a method for delivering secret information to a client as a posted letter. In the method, the information, such as a code, is printed and enclosed into an envelope on which the client's address information is printed. According to the invention, a print carrier (1) is provided for printing the secret code, such as a PIN number (2), and concealed client identification information (3) on a same printing surface; the print carrier is glued and folded to form a closed envelope (4) in such manner that the secret code is enclosed inside the envelope but the identification information remains visible; and the identification information is read and used for printing the client's address information (5) onto the closed envelope.