The Patent Law Treaty was drafted with the aim to 'streamline and harmonize' formal requirements set by national or regional Patent Offices for the filing of national or regional patent applications and the maintenance of patents. In this Article a number of core issues of the Patent Law Treaty has been selected: requirements for the accordance of a filing date, relief in respect of time limits and restoration of priority. A conclusion of this Article is that the goals of the Patent Law Treaty were not achieved by the Treaty as concluded. One of the reasons is that the Treaty contains too many optional requirements ('may require') which may be implemented as compulsory by the Contracting Parties, allowing them too much freedom when implementing requirements of the Treaty into their national and regional patent laws. This defies the aim of harmonization and streamlining of the Patent Law Treaty. The negotiation history is described and discussed with emphasis on what went wrong during the negotiations. Reasons for the failure of the Patent Law Treaty are discussed and recommendations for repair are given.