The overall gas exchange occurring between Mediterranean ecosystems and the atmosphere has been rarely quantified experimentally, but due to the occurrence of prolonged summer drought that limits gas exchange, the potential carbon (C) sink of Mediterranean ecosystems is generally considered low. Net Ecosystem C Exchange (NEE) was measured for a period of 12 months in the Island of Pianosa (Central Italy) using the eddy covariance technique. The Island is partly covered by macchia vegetation and by abandoned agricultural land and it is ideal for flux measurements due to its flat topography and for the absence of anthropogenic C sources. C-flux measurements made between April 2002 and March 2003 showed that the Island of Pianosa was a net sink of C during a 12 months period accumulating 2.64 t C ha-1 per year. Such a sink was less than what has been reported for evergreen forest in the region, but it is larger than what is generally estimated for drought limited ecosystems. The analysis of seasonal changes in the C-flux revealed that phenology and temperature were likely limiting C uptake during the winter months, while drought was limiting during the summer months. The potential C sink that could be provided by the entire island was finally calculated as the difference between the C stock contained at present in the Island's ecosystems and that contained in the areas covered by the Mediterranean macchia.