The UK and USA are currently undergoing a period of considerable change in their attitude towards medical error and their understanding of its causes and magnitude. In both countries, with increasing rapidity, a disturbing situation is being revealed. This paper presents the results of an investigation into medical errors in the UK and the USA, and focuses in particular on the magnitude and causes of errors when using medical devices. Contrary to the traditional approach of blaming users, it is suggested here that many such errors are caused partly by poor device design, which fails to account adequately for the needs of users. In response, this paper also discusses the basics of a Human Factors Engineering (HFE) approach as a step towards overcoming this problem and offers a challenge to device users and design companies (manufacturers) to follow HFE principles in order to improve the efficiency of operation and reduce errors during device use.