Different measures to reduce waiting time for elective treatment in the Norwegian specialist health service have been in place. In the period from 2008 to 2010 the Norwegian directorate for health introduced 32 priority guidelines to give guided priority to either an outpatient consultation or treatment for 398 conditions, and a specified maximum waiting time. The priority guidelines were developed by 32 national grops of experts under the supervision of the Norwegian Directorate for Health. The national groups of experts defined the relevant conditions by clinical criteria and not linked to ICD-10 codes (ICD = International Codes of Diseases). In the NPR-dataset ICD-10 codes are used and the expert groups assisted in identifiing the conditions by ICD-10 codes. The administrative data used from the Norwegian Patient registry (NPR) made it possible to perform before and after analyses, the so-called interrupted time series analyses. A limitation was changes in coding practice and the reduced level of registration in 2008 on the new reporting format for data from hospitals to NPR. In all 282 of 398 conditions of the priority guidelines are analysed. Several conditions lack defined codes, and for the guideline for a limited number of conditions were assessed. System change: Two guidelines showed a significant reduction in waiting times for all conditions included; and For 21 guidelines there was seen a varying degree of compliance with the guidelines. For six guidelines there were no significant changes in waiting time at the time of the introduction of the guidelines. Some non-prioritized conditions showed positive changes. Three were not analysed due to low numbers in 2008–2009. Breach of maximum waiting times: In 2012 19 conditions had 50% or more extended waiting times per referral. Out of 183 conditions 149 had a significant decreasing trend during the years 2010–2012, whilst 7 showed an increasing trend. Harmonization between health regions: The analyses show differences in waiting time between the four hospital regions by 81% of the 234 conditions tested.