When constructing a building, it is easy to forget that the success or failure of any project may rest on its indoor environmental quality (IEQ). Healthy and comfortable employees are often more productive especially considering that people spend 90% of their time indoors (LEED V4, 2014). The aim of this paper is to find out Indoor environmental quality factors that office building users are concerned with the most and to figure out which factors are having the greatest effect on their performance and satisfaction. The data analyzed and discussed in this paper was collected using an online self-assessment questionnaire. Self-assessment questionnaire is considered a method of applying post occupancy evaluation for a building, reliability of this approach is being relevant to everyday office work and can deal with descriptive, qualitative and subjective characteristics. Responses of 118 office occupants in Egypt showed that 32.7% voted for thermal comfort as the indoor environmental quality factor having the highest effect over their work performance. When asked about sources of dissatisfaction in the office environment, Problems related to visual comfort earned 36.1 % of the overall dissatisfaction sources, these problems were presented in the lack of having a window, window area is too small, insufficient daylighting, poor lighting levels, glare on computer screens, and lack of outdoor natural views within the workspace.