Mobile communication and wireless data transmission are playing an increasing role in health care. Reports describing medical device malfunction related to cellular phones have raised awareness about the problem of electromagnetic interference. Although initial institutional responses were to ban cellular devices in hospitals, these restrictions are relaxing as the knowledge base in this area expands. Medical device malfunction is extremely rare if the distance from the transmitting device is greater than 1 m. This article reviews the current understanding of electromagnetic interference as it applies to the technology-rich critical care environment.