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To investigate the changes in the structure and composition of the vegetation during the Pleistocene-Holocene transition, pollen and macrocharcoal analyses were carried out on samples of sediments taken from a 14.5m core from Hoya Rincon de Parangueo, a crater lake (maar) in Guanajuato, Mexico. Fossil pollen data from the core suggest that during the last glacial maximum (LGM) the climate in central Mexico was very wet and cold, and the vegetation was open cloud forest, and fires did not occur. During the Pleistocene-Holocene transition, vegetation diversity was high in the study area, but disturbance to vegetation was observed, indicating an open habitat with fewer trees. There was an abrupt change in the composition of the vegetation during the later Holocene, likely signalling a strong change in climate. During the early Holocene the area remained wet, but there was a trend toward drier conditions that became well established at the end of the middle Holocene and into the late Holocene. As a consequence, the structure of the vegetation changed, with more taxa suggesting dryer environments, lasting until the late Holocene, when human disturbance became an important factor affecting vegetation in the area.