Mt Parnitha is located in Sterea Ellas (Central Greece) and is the highest mountain in the vicinity of Athens. Its wild vascular flora comprises 1096 taxa belonging to 90 families, of which 122 taxa and four families are reported here for the first time. The endemic element comprises 92 Greek, 42 Balkan and 18 Italian–Balkan–Anatolian taxa. Four Greek and three Balkan endemics are new records for the mountain. The predominance of the Mediterranean element (63.6%) and the therophytes (37.6%) underlines the Mediterranean character of the mountain's flora. The endemic elements of Mt Parnitha are presented, their protection status is mentioned and the phytogeographical affinity with neighbouring mountains is examined. Three vegetation zones and 17 habitat types within them have been identified, and those facing threats are indicated. Although the mountain is a National Park, several factors influence its flora and vegetation, the most important being its proximity to Athens.