An aerial survey in June 1988 of highland Eucalyptus forests on the western slopes of the Great Dividing Range, between Canberra, A.C.T., and Cabramurra, N.S.W., revealed extensive light to medium defoliation of peppermint-gum forests, covering several thousand hectares. The defoliation was heaviest near the Corin Dam, where ground observations identified the cause of the damage as the spurlegged phasmatid, Didymuria violescens (Leach). It is suggested that the defoliation represents the start of a new outbreak, similar to that of the 1960s, which will increase in area and extend further south with each generation every 2 years causing defoliation in correspondence with the insects 2-year life cycle.