Emergency Department (ED) overcrowding is a national crisis with few prospective data to document its occurrence. The objective of this study was to prospectively collect data on variables involved in Emergency Department overcrowding (EMDOC) using an Internet-based data entry model. A prospective observational Internet-based study involving 18 hospitals over a 13-month period was designed. Investigators input data into the EmDOC Internet site at 10:00 p.m. on 7 random days each month. The study found that the primary reason for ED overcrowding was lack of inpatient beds. Important means were: patient-to-nurse ratio = 2.85, diversion was 7.4 h/24 h, and hospital census was 83%. From ED waiting room to an ED bed took a mean time of 209 min. The mean number of makeshift beds was 3.1. There was no single variable that was noted to define or predict overcrowding. Documentation of factors involved in ED overcrowding found that overcrowding was not just an ED problem, but a problem that occurs due to overcrowding in the entire institution.