In July 2021, the Electromagnetic Compatibility Conference Japan (EMCC) published a revised version of the "Guide for Safe and Secure Use of Radio Waves in Medical Institutions" (the "Guide"), which was primarily published in 2016. The 2016 edition of the Guide describes channel management methods, a simple measuring method of the electromagnetic environment (detailed methods are given in the appendix), examples of problems, countermeasures for medical institutions, and points of concern for wireless LAN network development and maintenance providers, for medical telemetry system, wireless LAN, and cellular phones, respectively. Since its publication, new standards of wireless LAN have become more widespread, and in 2017, EMCC presented a model of regulations that could be used by medical institutions. To meet them, the guide was revised. As for wireless LANs, adding to the description of 2016 edition, support for new standards (IEEE802.11ax or Wi-Fi6), support for "tethering," and management methods referring to the draft regulations were added. "Frequently Asked Questions" have also been added. Recently, the use of tethering using smartphones and mobile routers brought in by patients and visitors has been increasing. The new guide also mentions about management of tethering.