Surveys over a period of 38 years have shown a rapid successional change in the remaining areas of cerrado vegetation in western São Paulo State. Cerradão (the dense, tall, forest form of cerrado (sensu lato)) and cerrado/Atlantic forest ecotonal vegetation have replaced more open forms (such as campo cerrado) during this period. An aerial photographic survey in 1962 showed 75% cerrado (sensu stricto), 16% campo cerrado, and only 9% cerradão, while a survey combining Landsat imaging of 1992 with aerial photography of 1984 gave 69%, 0.6%, and 30.5% respectively for the same physiognomies. Visiting 10% of the sites of the latter survey in 2000 showed that cerradão had become the dominant vegetation of 68% of them. In a particular 180 ha site in Assis municipality, cerradão increased from 12.0 to 41.4% of the area in 22 years. Reduction of anthropic pressures, such as fire and cattle-grazing, is considered responsible for these rapid changes. Conservation issues and research priorities related to these changes are discussed and proposed.