Financial and real estate crises and 'the new way of working' reduce the need for office space, and office markets become replacement markets without a quantitative need for new office buildings: In the Netherlands, currently 15% of the office space is vacant, of which 60% is structurally vacant, without perspective of future tenancy. Despite the high vacancy, real estate advisors and office market experts expect the vacancy to continue rising: while new office buildings are still constructed, the take up of new space slows down and existing companies are expected to get rid of superfluous office space at their next contract agreement. However, other experts expect the hidden vacancy to reverse the trend of decreasing floor space to worker ratio.This paper aims to investigate and quantify the occurrence of 'hidden vacancy' and estimate the effect of 'hidden vacancy' on the office market, answering the following research questions: to which extent does hidden vacancy exist in the Dutch office market? How does it affect the office user in specific and the office market in general?To answer these questions, a survey was held among office organisations that intend to make accommodation decisions within the next 5 years. Henceforth, interviews were held with decision makers of large-scale corporate organisations and accommodation experts, discussing in-depth the influence of (hidden) vacancy on accommodation decisions.This study is part of an on-going study on changes of office user preferences and the effect of these changes on the office market and the built environment.