OBJECTIVES:  In cases of rare or severe diseases without alternative therapeutics, the French “Temporary Authorization for Use” (ATU) program allows the use and the reimbursement of drugs before their marketing authorization (MA). It creates a window of free prices in a highly regulated market. After the MA, the patient access is maintained during the market access process (HTA assessment and agreements on reimbursement and price). The objective of this work is to assess the economic impact of this post-ATU transition period (that has been reframed in 2014) and during which drugs begin to spread. METHODS: We included all drugs that experienced the post-ATU period from 2014 to April 2016 or that are still going through it thanks to the list established by the French authorities. We assessed the time spent during the post-ATU period and the financial impact for the 37 public hospitals of Paris (AP-HP). We collected explicative variables from different sources (orphan drug, target population, added medical benefit). RESULTS:  45 International Nonproprietary Name (INN) are on the post-ATU list. Within the 17 INN that were regularized since 2014, 6 of them were direct-acting HCV antivirals and 6 were orphan drugs. The average post-ATU period was 237 days. Only 6 (35%) remained less than 180 days. Within the 28 INN that still have post-ATU status, 17 (61%) are in market process since more than 180 days. 40/45 INN are referenced in AP-HP and have costed, during their post-ATU period, approximately €600 million since 2014 until today. In 2015, post-ATU drugs represented 12% (€181 million) of the drug budget. CONCLUSIONS:  Post-ATU drugs represent an important financial impact whereas these drugs are still under a derogation procedure. It seems that the market access procedures last longer than usual, as patient access is maintained, but for a higher financial risk for hospitals.