Yes, the Walt Disney World Marathon Weekend (typically held in early January) brings a significant spike in attendance, making the parks much more crowded than a standard winter week. While the races themselves start in the pre-dawn hours, the thousands of participants and their families spend the rest of the day in the parks. EPCOT and the Magic Kingdom tend to feel the most congested due to race finish lines and celebratory crowds. Beyond the physical crowd levels (which often hit 7/10 or 8/10), the weekend introduces logistical "invisible" crowds: road closures and transportation delays are common as runners cross major arteries within the resort property. Most race participants arrive a few days early rather than staying late, so the days leading up to the Sunday marathon are busier than the Monday and Tuesday following the event. If you are not participating in the race, you should prepare for longer wait times at popular attractions and make your dining reservations exactly at the 60-day mark to ensure you get a table amidst the influx of hungry "runDisney" athletes.