1510 first arrival times from regional distances (333-1600 km), in and around the Tibetan Plateau were inverted in a backprojection tomography study to map the lateral variation of Pn velocity structure within the mantle-lid. Accurate determination of the upper mantle velocity structure of the Tibetan Plateau is thought to be a key to understanding the tectonic evolution of this important region. Previous studies of regional Tibetan earthquakes have placed first-order constraints on upper mantle velocities, but have to rely on data recorded almost exclusively at stations outside of the plateau (Zhao and Xie, 1993; Ni and Barazangi, 1983; Beghoul et al., 1993). The increased resolution of our tomographic analysis is a result of 40 events with refined locations recorded at stations within the Tibetan Plateau (Randall et al., 1995). Using these 40 events, over 300 Pn arrival times were hand picked from digital recordings obtained during a one year deployment of broadband sensors on the Tibetan Plateau. Additional travel times, used to supplement the data set, were obtained from the International Seismological Center (ISC). We were able to extend our coverage by including Pn arrivals from additional plateau events, relocated in previous studies, recorded at stations in and around the Tibetan Plateau (Molnar and Lyon-Caen, 1989; Zhao and Helmberger, 1991). The large number of observations that we have obtained provides good resolution over most of the plateau and surrounding regions. Preliminary Images obtained in the study show an average Pn velocity lateral variations of about 4% that correlate well with major tectonic features and previous geophysical observations. Specifically the northern plateau is slow relative to the south. This same region has previously been recognized to inefficiently propagate high-frequency Sn phases. The coincidence of slow Pn and inefficient Sn propagation is strong evidence for the existence of partial melt within the uppermost mantle beneath the northern Tibetan Plateau. Our results suggest significant mantle variation between the northern and southern plateau that must be addressed in tectonic models describing the evolution of this important continental collision.