The terms 'telemedicine', 'telehealth' and 'e-health' are often used interchangeably. We examined the occurrence of these terms in the Scopus database. A total of 11,644 documents contained one of the three terms in the title or abstract. Telemedicine was the most common term, with 8028 documents referring to it, followed by e-health (n = 2573) and then telehealth (n = 1679). Telemedicine was referred to in documents from 126 countries; the terms telehealth and e-health were found in publications from 55 and 99 countries, respectively. Documents with telemedicine in their title or abstract first appeared in 1972, and continued to appear at a low rate until 1994 when they started to increase rapidly; telehealth showed a similar pattern, but with the growth beginning about five years later. Although articles containing the term e-health appeared later than the other two terms, the rate of increase was higher. Articles (journal papers) were the most common type for the three key terms, followed by conference papers and review articles. Publication rates for telemedicine or telehealth or e-health were compared with two other relatively new fields of study: Minimally Invasive Surgery (MIS) and Highly Active Antiretroviral Therapy (HAART). Publications concerning HAART seem to have reached a peak and are now declining, but those with the three key terms and those concerning MIS are both growing. The variation in the level of adoption for the three terms suggests ambiguity in their definition and a lack of clarity in the concepts they refer to.
