Distraction from the background environment while performing concentrationdemanding tasks is a common issue for office employees in shared work areas. However, few field studies have been conducted on the effects of different office types and work areas on objective measurements of cognitive performance. The first aim of the present field study was to investigate, before relocation to an activity-based workplace (ABW), differences in performance on a concentration-demanding cognitive task between individuals in shared/open-plan offices compared to cell offices. The second aim was to investigate, after relocation, how performance differs (withinperson) between different work areas within the ABW. This study included employees from five offices (n = 113), of which four relocated into an ABW. An acoustician measured the equivalent sound levels of the work areas. Data were analyzed using linear regression (aim 1) and mixed models (aim 2). Before relocation, employees working in shared/open-plan offices performed significantly worse (14%) than those in cell-offices, which had a 15 LAeq lower noise level. After relocation, employees performed significantly worse in the active zone without noise restrictions, compared to all other work areas. When shifting open-plan area from the active zone to the quiet zone cognitive performance increased significantly by 16.9%, and switching to individual working rooms increased performance by 21.9%. The results clearly demonstrate the importance for organizations to provide quiet areas or rooms with few distractions for employees working on tasks that demand concentration in an ABW. A daily drop in performance for each employee may be expensive for the organization in the long run.