Catalogue of endemic, rare or threatened vascular plants in Catalonia. I. Endemic taxa. This is the first of a set of papers devoted to rare or threatened plants in Catalonia. We list 279 specific or subspecific taxa which are in a broad sense endemic to the northeastern part of the Iberian Peninsula. We assess them with regard to their conservation status according to IUCN criteria. Assignment of these taxa to established categories has led to the following results: 6 taxa critically endangered (CR), 5 endangered (EN), 32 vulnerable (VU), 5 near threatened (LR nt). 84 least concern (LR lc), 116 not threatened (NT) and 31 data deficient (DD). The small number of taxa that enjoy legal protection in comparison with the number of threatened plants is emphasized. Key words: Endemic plants, Catalonia, Plant conservation, UICN categories.