Nice short article in Healthcare Informatics on WLAN security. Written by Bob Hedglen at UPMC, he details the risks and provides a nice summary of the requirements:

We decided our WLAN installation required a documented security policy,
use of data encryption, authentication of every device and user,
verification of ongoing policy enforcement and security incident
reporting. The system had to complement the WLAN engine from Cisco, San
Jose, Calif., to manage and support dynamic communication between our
more than 500 existing access points and the many more we expected to
have. We needed a vendor-neutral system to monitor our environment and
protect our network and data.

UPMC chose the vendor AirDefense
for a WLAN network appliance. The new WLAN switches from Aruba,
Trapaze, Symbol and now Cisco (via their AireSpace acquisition) include
most if not all the features of a separate WLAN security appliance. As
Bill describes, UPMC already had 500 accesspoints, so a network
appliance was the best fit for them.