Background: This study presents the native flora of Mountain Panachaikon (N.W. Peloponnese, Greece), after extensive field work (from ~700 to 1900 m) and critical literature review. Results: The vascular native flora of Mt. Panachaikon comprises 757 taxa, 95 of which are Greek endemics, 79 are Balkan endemics, while 229 taxa are reported here for the first time. The known distribution of the Greek endemics Alyssum montanum subsp. montanum var. graecum, Carum heldreichii, Cirsium heldreichii, Genista milii, Minuartia eurytanica and Seseli parnassicum is expanded, being reported for the first time for the floristic region of Peloponnese, and the number of the known populations of the Near Threatened Gymnospermium altaicum subsp. peloponnesiacum is increased. Conclusions: The study area appears to have the second highest endemism and the highest one in W. Greece, compared with other mountains of N. Peloponnese and Sterea Ellada, while 22.10% of the endemics are protected and/or evaluated as Near Threatened to Endangered. It also exhibits a rather high proportion of Balkan endemics, in relation to its geographic location, and some genuine arctic-alpine taxa. These indicate that Mt. Panachaikon can be rendered as a plant diversity hotspot in the Peloponnese.