Faculty of Business, McMaster University, Hamilton, Ontario The present study of size-structure relationship is based on a sample of 168 United States life insurance companies. Data were collected on three measures of organization size and four measures of structure. In view of the high intercorrelations among the three size measures (r> .87), only one was used in subsequent analysis of size-structure relationship. The results indicate the relationship to be highly significant but nonlinear. In general, the structure differentiation tends to increase with size but at a decreasing rate. The study also compares the size-structure relationship across small, medium, and large organizations. These results point to a varying dimensionality of organization structure at different size levels.