Evidence for early agriculture can be obtained from pollen profiles indicating forest clearance1. The practice of cultivation is widely believed to have been introduced into the interlacustrine region of central Africa by Bantu-speaking iron-workers2, present by 2,000 yr BP (ref. 3) or, disputedly2–4, 2,600 yr BP (ref. 5). There are, however, archaeological and linguistic indications that cultivation may have begun earlier3,4,6,7. Published pollen diagrams which clearly show forest clearance in East Africa are either poorly dated8 or place forest destruction1 after 2,000 yr BP; possible palynological signs of previous clearance9,10 are open to other interpretations, notably climatic change1. We have now analysed the pollen and charcoal of a peat core from Ahakagyezi Swamp in south-west Uganda using radiocarbon for dating. The results suggest a history of forest clearance stretching back beyond 4,800yr BP. This is the earliest evidence for cultivation reported from tropical Africa.