The age of tropical secondary forests was estimated using a post-classification comparison of a multi-temporal sequence of Landsat sensor imagery for an area north of Manaus, Brazil. Five stages of regenerating secondary forest together with primary forest and agricultural land were identified. Most secondary forests at this site were younger than 14 years and therefore represented the regeneration stages at which carbon accumulation was at a maximum. This study has implications for the regional or global mapping of tropical secondary forests for global carbon studies.