Inventory data and general woody floristic lists are presented for northern Peruvian seasonally dry tropical forests (SDTFs). These preliminary data record ca. 250 woody species for the SDTFs around Tumbes, the inter-andean valleys and around Tarapoto. High levels of endemism are shown in these SDTFs, with between 13-20% of their tree species recognised as narrow regional endemics. A comparison of disjunct SDTF patches on the Pacific coast, in the Marañon drainage and around Tarapoto reveals only low floristic similarity (ca. 2-10%) between them, suggesting considerable barriers to species movement. Present day barriers arc represented by the Eastern and Western Andean Massifs. However, an examination of the disjunct species distribution patterns suggest that either species migration between the Marañon drainage and the Pacific region over the Andes has recently occurred via the Porculla Gap, or these areas were once continuous before the uplift of the Andes. A comparison of Peruvian dry forest plot data with inventories from southern Ecuador and Bolivia indicates that the northern Peruvian Tumbes and Marañon dry forests, and those of southern Ecuador may constitute a distinct phytogeographical unit.