The South-Eastern Norway regional health authority [Norwegian: Helse Sør-Øst] has implemented a large hospital reform in Oslo by merging four hospitals – creating Oslo University Hospital (OUS). This merger process is essential as background information to understand the measures conducted for efficiency improvement at hospital department level, which is the main topic of this master thesis. In 2004, the Ear-Nose-Throat (ENT)–departments at Ullevål and Rikshospitalet merged, in practice by gathering all personnel and equipment at one location (Rikshospitalet). Increasing the proportion of day surgery was one of the changes implemented in the reorganization process after the merger; another was assessment of ENT-cancers to a larger extent on daily basis [Norwegian: dagutredning], instead of hospitalization that had been the case previously. This is referred to as day assessment in this paper. Regarding day surgery, the specific ENT-department has developed and established a special, almost unique, expertise on performing cochlear implant operations without hospitalization, and this type of day surgery will be discussed in the thesis. It was considered interesting to compare two separate years after the department-merger in 2004, but before and after the reorganization process in the merged department, and the years 2005 and 2012 were chosen. Hence the intention was to study efficiency before and after implementation of measures expected to improve efficiency, such as a higher proportion of day surgery. By choosing these years the analysis has, however, not compared the period before and after the department merger, as both years studied are after the merger. Included in analysis and results are activity-data (mainly as DRGs) as well as input measured as FTEs (full-time equivalents/one year full-time-work). The plan has been to measure technical- and cost-efficiency, and analyze whether changes in these parameters correlate with the measures implemented during the reorganization process at the department, and discuss if there is a relationship. The analysis has shown that there has been a substantial increase in the proportion of day surgery in the ENT-department, and that efficiency measured as cost-efficiency are much better in 2012 compared to 2005. Technical efficiency is almost equal according to the analysis performed in this study. Reasons for these changes will be discussed, as well as a discussion of uncertainty in the results.