We use nearly 2100 P-wave arrival times from 166 local earthquakes to investigate the 3-D compressional velocity structure of the upper crust of Slovenia using the simultaneous inversion algorithm developed by (Michelini and McEvilly, 1991). Remarkable and stable features of the resolved model are the relatively high velocities in western Slovenia and the low velocities in central Slovenia, SE of the Ljubljana basin. The boundary between these two anomalies follows approximately the NNW-SSE direction that coincides with the general strike of the External Dinarides. We interpret this feature as the upper crustal expression caused by the tectonic processes occurring along the active margin of the Adria promontory/microplate.