Annual and monthly air temperature were analyzed at meteorological stations covering nearly the whole vertical range (696 – 2 636 m a. s. l.) of the High Tatras Mountains over the period 1961 – 2007. Upper-air temperature measurements from a nearby aerological station were interpolated to correspond to the altitudes of the participating ground stations. The aim of this study was to evaluate the long-term variability in the air temperature at different altitudes using two independent data sources. In spite of systematic differences between ground and upper-air temperatures, the comparison between homogenized time series showed a tight correlation and identical periods of increase or decrease in both data sets. The same periodicities, identical coolest and hottest years, similar shifts in annual and monthly temperature distributions and increase in selected isotherm altitudes were found in the period 1991 – 2007 when compared to the climatic normal 1961 – 1990. Statistically significant linear trends in annual temperature in the range from 0,21 °C/decade to 0,30 °C/decade were detected in both data sets. The steepest increase in the temperature was found in July, August, December and January. The altitudes of selected isotherms were calculated by two methods: (1) linear fitting and (2) cubic spline interpolation of the vertical temperature profile. Particular combinations of data sources (aerological and ground) and calculation methods (linear fit and cubic spline) gave slightly different altitudes for selected isotherms. The method used to calculate the isotherm altitudes should be taken into consideration when comparing results from previous studies. Linear increasing trends in the altitudes of selected isotherms of annual temperature in the range 3,9 m.year-1 – 5,2 m.year-1 and 2,5 m.year-1 – 4,9 m.year-1 were calculated for aerological and ground data, respectively. A significant increasing linear trend in the selected monthly temperature isotherm position was found only in July and August. An increase in isotherm altitudes indicates a shift in the vertical climatic stratification.