After a long absence from taxonomy, I accepted a contract to revise Diospyros for the Tree Flora of Sabah and Sarawak in July 1999. The last comprehensive revision of Diospyros that covered Borneo was Bakhuizen van den Brink’s Revisio ebenacearum malayensium [Bull. Jard. Bot. Buitenzorg III, 15 (1936-1941) 1-515]. In the present revision, 22 species are reduced to synonymy and 12 new taxa will be described. This brings the total number of confirmed species in Borneo to 78. Another 8 species cannot be resolved until I can examine their types, because all other evidence available is insufficient to support decision-making. Of these 78 species, 33 (42%) are endemic to Borneo. Within Borneo, most range across political boundaries. Consequently, Sarawak has only 8 endemics, Sabah has 5, Kalimantan 2, and Brunei none. However, Brunei has D. yeobii, which occurs nowhere else in Borneo, but is found on the other side of the South China Sea, in Peninsular Malaysia. The level of endemism will certainly drop if Diospyros is revised for the Philippines and E Indonesia. Indeed, the revision of Diospyros for Borneo had a spill over effect on the status of Diospyros in Peninsular Malaysia (which I had revised for the Tree Flora of Malaya in 1978). Four peninsular species had to be reduced to synonymy and the number of peninsular endemics dropped from 23 to 17 due to extension of their known ranges to Borneo.