Abstract : The ANTARES collaboration is building a high energy neutrino telescope in the Mediterranean sea, 40 km off La Seyne sur mer in France. The goal of the experiment is to detect high-energy cosmic neutrinos using a 3D array of 900 photomultipliers held by 12 strings. The detection principle relies on the observation, using photomultipliers, of the Cherenkov light emitted by charged leptons induced by neutrino interactions in the surrounding detector medium. Since December 2007, the ANTARES detector comprises 10 strings, a total of 750 optical detectors, connected to the shore via an undersea cable from the site at a depth of 2475m. First studies of the detector performance are detailed and preliminary results for the reconstruction of downward going cosmic ray muons as well as the observation upward going neutrino candidates are presented.