A study has been undertaken of minimum and maximum temperature trends this century for a number of climatological observing sites in Switzerland, typical of both the lowlands and the Alpine domain. Detailed analyses for each month of the year highlight differences in trends between the autumn-winter period and the late spring-early summer period. In the former case, minimum temperature trends are observed to increase by 2.5°C /century, while in the latter, maximum temperature trends are seen to decrease by more than -0.5°C /century. The changes in temperature characteristics exhibit a general decrease in the diurnal temperature range, a feature which has been observed in other independent studies. In addition, the variability of winter temperature decreases as the means increase. In terms of the potential impacts on forests, the present results imply a lengthening of the vegetation period and an increase in the potential for vegetation to live at higher altitudes and in greater numbers than the increase in average temperatures alone would imply.