An index for indoor environmental quality, the Indoor Environmental Index (IEI), was developed. This study aggregates the Indoor Air Pollution Index, an index found in the literature, and a new index: the Indoor Discomfort Index. The average of these two indices is the IEI, which is calculated using concentrations of eight pollutants and two comfort variables measured in 100 office buildings in the United States. The database used was developed for the U.S. Environmental Protection Agency Building Assessment Survey Evaluation study. A symptom index also is developed to denote persistent occupant symptoms. The IEI and the symptom index are used to investigate the relationship between indoor environmental quality and symptoms. Two simple linear regression models were formulated; these models explain 67 and 79% of the variation in the average symptom index, with the variation of the average IEI depending on the method of averaging used in the construction of the models. In addition, a conceptual explanation is provided for the empirical or regression models formulated. The IEI and the associated models relating indoor environmental quality with the office occupant symptom index may be used as management tools, as illustrated with an example.