The Orchidaceae outnumber by far any other plant family in Malesia. At present, however, an accurate estimate of the number of Malesian orchid species is difficult to make. Subtracting the number of established synonyms from the number of names attributed to Malesian orchid species results in the staggering figure of 6414 species, with a retention ratio (ratio of ‘accepted’ species to heterotypic names) of 0.74. This is undoubtedly a gross overestimate, as most of the 209 Malesian orchid genera have never been revised over their entire range. Extrapolating from available revisions to estimate a more realistic retention ratio is problematic due to the small number of modern revisions and the different nature of the groups treated. If we look for comparison at Malesian species of some recently revised groups, we encounter a wide range of retention ratios: Bulbophylluw sect. Uncifera (Vermeulen, 1993): 0.24 Dendrobium sect. Oxyglossum (Reeve & Woods, 1989): 0.24 Mediocalcar (Schuiteman, 1997): 0.29 Pholidota (De Vogel, 1988): 0.29 Bulbophyllum sect. Pelma (Vermeulen, 1993): 0.50 Paphiopedilum (Cribb, 1987, modified): 0.57 Dendrobium sect. Spatulata (Cribb, 1986, modified): 0.60. Correspondingly, we find a wide range of estimates for the ‘real’ number of known Malesian orchid species: from 2050 to 5125.