Information about queue length is an important parameter for customers who face the decision whether to join a queue or not. In this paper, we study how optimal information disclosure policies can be used by a service provider of an class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0167637715001649&_mathId=si12.gif&_user=111111111&_pii=S0167637715001649&_rdoc=1&_issn=01676377&md5=e60dab67628a5089be7d333cbdb7d0ba" title="Click to view the MathML source">M/M/1class="mathContainer hidden">class="mathCode"> queue to increase its revenue. Our main contribution is showing that the intuitive policy of informing customers about the current queue length when it is short and hiding this information when it is long is never optimal.