Balance of payments systems all over the world can roughly be cate-gorised in two - settlement-based systems and survey-based systems such as the Danish. This paper deals with the selection of the Danish survey and the grossing-up estimation. Focus, however, is on the Danish methods of survey maintenance over the medium term insuring both high total survey coverage and broad coverage in terms of instruments and sectors. Many countries with survey-based systems confront similar challenges and the working paper can hopefully be of inspiration and generate discussion. In the Danish system equity, intercompany debt, etc., loans and deposits, other investments, trade credits and financial derivatives are survey-covered for the sectors non-financial corporations, other financial intermediaries and insurance and pension funds. Using a dynamic register on financial account data and simple statistical methods the survey coverage on equity is maintained and the grossing-up is dynamically re-estimated. For intercompany debt, etc., loans and deposits, and other investments a method has been developed to maintain coverage over time while grossing-up is assumed constant. Trade credit coverage and grossing-up is maintained by a very sim-ple method using foreign trade statistics. Derivatives and financial leasing are assumed covered by the survey.