This paper investigates the electromagnetic compatibility of 45 critical care medical devices (infusion pumps, defibrillators, monitors, lung ventilators, anesthesia machines and external pacemakers) with various types of wireless local area network (WLAN, IEEE 802.11 b/g, 2.45 GHz, 100 mW) adapters. Interference is evaluated by performing ad-hoc tests according to the ANSI C63.18 recommended practice. The behavior of the devices during the tests was monitored using patient simulators/device testers specific for each device class. Electromagnetic interference cases were observed in three of 45 devices at a maximum distance of 5 cm. In two cases the interference caused malfunctions that may have clinical consequences for the patient. The authors' findings show that the use of these wireless local area network adapters can be considered reasonably safe, although interference may occur if they are operated at very close distance (<10 cm) to the medical devices.