A serious decline of mukwa (Pterocarpus angolensisDC.), a timber tree of considerable economic importance, has caused concern in parts of southern Africa for many years. Dieback and deaths have variously been investigated in the past and attributed to a succession of drought years. A new and discrete vascular wilt disease, characterised by a combination of distinctive crown symptoms with streaks of vascular discolouration in the youngest sapwood, is described from Zambia.Fusarium oxysporumSchlect is provisionally regarded as the causal organism. The widespread decline phenomenon is interpreted in the light of this disease which is named mukwa wilt and now dominates the pathology of mukwa, and is the most important disease of an indigenous tree species in Zambia.