||The widespread use of wireless telecommunications devices, particularly mobile phones, has resulted in increased human exposure to radiofrequency (RF) fields. Although national and international agencies have established safety guidelines for exposure to RF fields, concerns remain about the potential for adverse health outcomes to occur in relation to RF field exposure. The extensive literature on RF fields and health has been reviewed by a number of authorities, including the Royal Society of Canada (1999), the American Cancer Society (2001), the European Commission’s Scientific Committee on Toxicity, Ecotoxicity and the Environment (2001), the British Medical Association (2001), the Swedish Radiation Protection Authority (2002), and the Health Council of the Netherlands (2002). This report provides an update on recent research results on the potential health risks of RF fields since the publication of the Royal Society of Canada report in 1999 (J. Toxicol. Env. Heal., B4, 1-143) and our previous 2001 update (J. Toxicol. Env. Heal., B4, 145-149), covering the period 2001-2003. The present report examines new data on dosimetry and exposure assessment, thermoregulation, biological effects such as enzyme induction, and toxicological effects, including genotoxicity, carcinogenicity, and testicular and reproductive outcomes. Epidemiological studies of mobile phone users and occupationally exposed populations are examined, along with human and animal studies of neurological and behavioural effects. All of the authoritative reviews completed within the last two years have concluded that there is no clear evidence of adverse health effects associated with RF fields. At the same time, these same reviews support the need for further research to clarify the possible associations between RF fields and adverse health outcomes that have appeared in some reports. The results of the ongoing WHO study of mobile phones will provide important new information in this regard.