A mobile medical information system, developed primarily for the purposes of civilian medicine, is expanded to be used in military medicine. A usability study with 7 military physicians at the Finnish Defense Forces was conducted in field conditions in December 2005. Their evaluation of the characteristics and the features of the system, and properties and the features of the mobile device-Nokia 9210 Communicator were investigated. The results show that both the mobile system and the device have some degree of readiness for military medicine. Further usability improvements of the system and the device are discussed.