In 1971, the UFK-scale was presented as rarity scale for the Dutch flora. It is based on occurrences of vascular plant species on a national grid of 5×5 km2. More detailed information on plant occurrences based on a national grid of 1×1 km2 has become available since. In this article the KFK-scale is presented as a new rarity scale for the Dutch flora based on more detailed botanical information. For each of the 1490 Dutch plant species the KFK is presented for three periods in the 20th century: 1902–1950, 1975–1987 and 1988–1999. The results of 30 common, 30 most strongly increasing, and 30 most strongly declining plant species are presented.