The Perrier's sifaka Propithecus perrieri, considered critically endangered by the IUCN (World Conservation Union; 2004), is one of the least studied and most endangered primates in the world, yet baseline information on its distribution and population levels has not been updated for over 10 years. Density estimates from former studies suggest that only between 100 and 2000 individuals remain in the wild. In 2003–2004, using the line-transect method, information on the distribution and population levels of this and sympatric primate species were obtained. Multi-spectral, Landsat 7 satellite images of areas comprising the known Perrier's sifaka distribution, acquired in 1994 and 2002, were compared using spatial analysis techniques to quantify regional patterns of deforestation. Results from this study indicate that the global population of the Perrier's sifaka consists of about 915 individuals and the effective population size is unlikely to exceed 230 individuals. Furthermore, an annual deforestation rate of 1.2% was detected in the only protected area where this species occurs. Deforestation, the decline of taboos against hunting and human immigration patterns influence primate population status in northern Madagascar and threaten to drive the Perrier's sifaka to extinction in the near future.