Nowadays, the study of the upper atmosphere is increasing, mostly because of the need to understand the patterns of Earth's atmosphere. Since studies on global warming have become very important for the development of new technologies, understanding all regions of the atmosphere becomes an unavoidable task. In this paper, we aim to analyze the temperature variability and its trend in the mesosphere and lower thermosphere (MLT) region during a period of 12 years (from 2003 to 2014). For this purpose, three different heights, i.e., 85, 90 and 95 km, were focused on in order to investigate the upper atmosphere, and a geographic region different to other studies was chosen, in the southern region of Brazil, centered in the city of Santa Maria, RS (29 • 41 02 S; 53 • 48 25 W). In order to reach the objectives of this work, temperature data from the SABER instrument (Sounding of the Atmosphere using Broadband Emission Radiometry), aboard NASA's Thermosphere Iono-sphere Mesosphere Energetics Dynamics (TIMED) satellite, were used. Finally, two cases were studied related to distinct grids of latitude/longitude used to obtain the mean temperature profiles. The first case considered a grid of 20 • × 20 • lat/long, centered in Santa Maria, RS, Brazil. In the second case, the region was reduced to a size of 15 • × 15 • in order to compare the results and discuss the two cases in terms of differences or similarities in temperature trends. Observations show that the size of the geographical area used for the average temperature profiles can influence the results of variability and trend of the temperature. In addition, reducing the time duration of analyses from 24 to 12 h a day also influences the trend significantly. For the smaller geographical region (15 • × 15 •) and the 12 h daily time window (09:00–21:00 UT) it was found that the main contributions for the temperature variability at the three heights were the annual and semi-annual cycles and the solar flux influence. A smaller trend (−0.02 ± 0.16 % decade −1) was found at 90 km height and small positive trends (0.58 ± 0.26 % and 0.41 ± 0.19 % decade −1) were found at altitudes of 85 and 95 km, respectively.. Keywords. Atmospheric composition and structure (middle atmosphere – composition and chemistry; pressure density and temperature) – meteorology and atmospheric dynamics (climatology)