When the « debt crisis » started in 1982, some observers feared that the worldwide recession could bring about a large scale financial crisis. Although the events after 1983 have in some respect reassured the banking community, the debt ratios of many developing countries remain high and make the financial krack syndrom periodically reappear. However, unlike what happened in the thirties, international creditors have avoided the occurrence of generalised defaults, thanks to rescheduling procedures. Thus, a direct appraisal of the losses suffered by the banking system in the eighties is in principle impossible. This paper elaborates an indirect method to estimate these losses, with the help of a survey representing the subjective beliefs of bankers about the assumed risks. After having assessed the size of the problem by a look at the recent evolution of the international debt and the international assets of industrialised countries, we shall see how the theoretical literature enlighte as the creditor-debtor relationship. Then, a quantitative method for assessing risks and a valuation of international banks' portfolios will be proposed. Such a method, as far as we know unprecedented, must be hold as experimental. It is a first step towards an estimation of industrialised countries' net external position, taking account of default risks. We are thus interested in the first place in these countries' point of view, and shall not try to elaborate a diagnosis of the debt problem, which would imply an examination of the welfare consequences of debtors' adjustement policies.