The analysis notes that Dutch policy is reactive; capacity depends on the sum of detention sentences. The interaction between the judicial system and its political embedding leads to a continuous growth in detention capacity. This spinoff process is also active when crime is not increasing. As a result, continuation of this growth is likely. Nevertheless, it is not clear whether judges allow capacity to affect the length of the prison sentences they impose. If so, a spiral process is taking place. In theory, this spiral could go downwards, and a proactive government policy could lead to reduction in capacity. However, as it is not clear that this is the case, it is concluded that detention capacity could best be reduced by ad hoc measures such as legalizing drugs. Figures and reference notes (Author abstract modified)