Currently, climatic changes are among the most critical issues because of their impact on health (high mortality rate) and their heavy influence on the economy. They induce global warming, leading to a surge of heat and cold waves, storms and floods. Our study aimed to study the tendency of the average temperature and the incidence of heat and cold waves in Tunisian cities. We collected daily minimum and maximum temperatures for seven governorates from different bioclimatic areas between 1991 and 2011. We calculated the average daily and annual temperatures. A heat wave was considered when the mean temperature exceeds the 90th, 95th, 98th and 99th centiles of mean temperature for at least 2 consecutive days. A cold wave was retained when the mean temperature is under the 10th, 5th, 2nd and 1st centiles of mean temperature for at least 2 consecutive days. The annual trend was assessed using the Mann–Kendall test for trend in R software version 4.1.0. The maximum temperature ranged from 46 °C in Siliana to 48.8 °C in Tozeur, and the minimum temperature was between −7 °C in Jendouba and 45.7 °C in Gabes. Tunis had the longest heat waves, while the number of days of cold ones was higher in Jendouba. For the 90th percentile, the number of heat wave days exceeded 20 days in all governorates during July and August 2003. We demonstrated a significant tendency in increase of the annual average temperature in four cities: Gabes (tau = 0.324, 2-sided p value = 0.042), Kairouan (tau = 0.325, p value = 0.039), Monastir (tau = 0.450, p value = 0.004) and Siliana (tau = 0.333, p value = 0.036). This increase was not significant in Tunis, Jendouba and Tozeur. This study showed the evidence of an increase in mean annual temperature in Gabes, Kairouan, Monastir and Siliana and the increase in the frequency of heat waves in the capital Tunis and cold waves in Jendouba city.