Tenerife (Canary Islands, Spain) is 2,034 km² in size and has a highest point of 3,718 m (Mt Teide volcano). It is the largest of the islands of the Canarian archipelago, which is situated off the coast of Africa and very close to the Tropic of Cancer. The island's climate varies greatly depending on height and also on the side of the island, due largely to the influence of the trade winds, altitude and the orientation of the mountain ranges. The northern side is considerably more humid than the south. Teide National Park is situated above 2,000 m and extends over an area of 18,990 ha. The main climate features, as measured at a weather station located at 2371 m, are as follows: mean annual air temperature of 9.6ºC, with major day-night fluctuations (temperatures can exceed 40ºC by day and fall by night to several degrees below zero); annual rainfall is between 400-800 lm^-2, with five dry months; low relative air humidity and constant winds, which can reach 200 kmh^-1 on occasions. The present paper aims to ascertain the temperature regime of the soil (Orthents) of the upper parts of Mt Teide and determine the influence exerted by orientation. To this end, two HOBO H8-type sensors were placed at 50 cm depth in two sites situated at 3,345 and 3,480 m on the north and south sides respectively. Readings were taken continuously over a period of one year, from September 2003 to August 2004. The results are spectacular. Despite the proximity to the Tropic of Cancer, the height of the Teide volcano is sufficient to ensure that the mean annual soil temperature is below 8ºC on both faces. On the north face, the mean annual temperature is 5.1ºC, while on the south face it is 6.6ºC. The summer mean (June, July, August) is below 15ºC (12.9ºC and 9.5ºC). The difference between the two faces lies not so much in the mean annual temperature as in the year-round contrasts. Whereas the isotivity (difference between the summer and winter means) on the north face is 13.2ºC, it is just 4.8ºC in the south. During the winter of 2003-2004 temperatures of below 0ºC were recorded on the north during four months –from mid-December 2003 until mid-April 2004. On the south side, the temperatures remained above 0ºC at all times, the lowest recorded being 2.5 ºC. The variability of the recorded temperatures is greater in the north than in the south, as reflected by the standard deviation of the data series (5.7ºC compared to 2.7ºC). The soil's biological activity slows down when the soil temperature falls below 5º C, a situation which arises on both faces of Mt Teide. Temperatures below 5º C are recorded constantly on the north face between 22 October 2003 and 9 May 2004 and on the south side from 11 February until 9 May 2004. From the data obtained, it is concluded that the soil temperature regime is cryic, given the absence of an O horizon. This is the first time the regime has been defined in these latitudes and in the Canary Islands.