In the summer 2000–01, thermal monitoring of the permafrost active layer within various terrestrial sites covered by lichen, moss or grasses was undertaken at Jubany (King George Island) and Signy Island in the Maritime Antarctic. The results demonstrated the buffering effect of vegetation on ground surface temperature (GST) and the relationship between vegetation and active layer thickness. Vegetation type and coverage influenced the GST in both locations with highest variations and values in the Deschampsia and Usnea sites and the lowest variations and values in the Jubany moss site. Active layer thickness ranged from 57 cm (Jubany moss site) to 227 cm (Signy Deschampsia site). Active layer thickness data from Signy were compared with data collected at the same location four decades earlier. Using a regression equation for air temperature versus ground surface temperatures the patterns of changing air temperature over time suggest that the active layer thickness increased c. 30 cm between 1963 and 1990 and then decreased 30 cm between 1990 and 2000. The documented increased rate of warming (2°C ± 1) since 1950 for air temperatures recorded in the South Orkney Islands suggests that the overall trend of active layer thickness increase will be around 1 cm year−1.