Bridges are an essential part of the transport infrastructure. A considerable number of these bridges are metallic, in many cases exceeding 100 years of age having suffered deterioration from environmental attack such as atmospheric corrosion. In order for infrastructural managers to make informed decision in terms of life-cycle cost perspective, reliable prediction of the remaining strength and service life of deteriorating bridges is essential. Deterioration models have been developed over the years to predict long-term material loss under different atmospheric conditions and environments. The aim of this paper is to quantify the effects of long-term deterioration, based on these models, on the remaining strength of metallic bridge girders, comprising of a number of plates. To obtain a useful insight into this problem, the finite element method is employed. In this paper, different plate elements, of varying slenderness and boundary conditions and representative of real bridge configurations, are analysed under different deterioration scenarios, brought about through material loss at different locations of the element. The effects of various parameters such as the degree/severity of material loss and the corrosion pattern (uniform versus non-uniform) on the buckling strength of the plates are quantified through both linear eigenvalue and non-linear analyses. The results of this study show that critical buckling strength of web panels may significantly drop at higher percentages of corrosion degradation and patterns, with the failure mode likely to change with increased deterioration. Differences between the critical buckling stresses obtained from the linear and non-linear analyses are presented.