Rumors suggesting the two devices would be close enough in design to share cases were correct -- existing iPhone cases designed to fit an iPhone 5 or 5s will also fit an iPhone SE.
Product listings for iPhone 5 and 5s cases, screen protectors, and other accessories on Apple's online store have all been updated to note their compatibility with the iPhone 5, 5s, and SE. Customers who previously owned an iPhone 5s and are planning to purchase an iPhone SE will not likely need to purchase new cases for the device.
The iPhone 5s has been discontinued in favor of the iPhone SE, and pricing on the new device starts at $399 for the 16GB model. Apple will begin accepting orders for the iPhone SE on Thursday, March 24, with an official launch coming on March 31.