Performance of Endcap Muon System of the Compact Muon Solenoid

The Endcap Muon System of the Compact Muon Solenoid (CMS) detector for the Large Hadron Collider will provide muon identification, momentum measurement, and Level-1 trigger. A $60^\circ$-sector of CMS was taking cosmic ray data in summer-fall 2006. In this report, we present results of muon detection efficiency and precision as obtained in situ during these tests.