The November 12, 1999 D¿zce earthquake ruptured a ~40-km-long fault segment of the North Anatolian fault system immediately to the east of the August 17, 1999 Izmit rupture. We use displacements of 32 sites derived from GPS measurements immediately before and after the D¿zce earthquake to estimate the geometry and slip distribution of the coseismic rupture. The ~51¿ northward dipping rupture plane, the rake of the slip vector (average 3.76¿0.04 m right-lateral, 0.76¿0.04 m normal slip), and the slip distribution inferred from the GPS data are consistent with seismic observations and the distribution of surface offsets measured in the field. The geodetically determined moment magnitude is Mw=7.2. The D¿zce earthquake had the highest slip-to-rupture-length ratio of any historic earthquake along the North Anatolian fault. This is consistent with the D¿zce earthquake being a part of a composite rupture with the preceding Izmit event. ¿ 2001 American Geophysical Union