A stent deployment device includes a flexible, elongate interior catheter and a retaining structure cooperating with the catheter to support a stent along a distal end support region of the catheter. The stent is supported in a reduced radius delivery state to facilitate delivery to a treatment site in a body lumen, by advancing the device over a previously positioned guidewire. An opening at the distal end of the device receives the guidewire into a guidewire lumen of the interior catheter. A second opening through the catheter wall just proximally of the support region allows passage of the guidewire to the exterior of the catheter, whereby the guidewire is contained within the device only along the distal end region. The retaining structure can include an exterior catheter surrounding the interior catheter and stent, and moveable axially relative to the interior catheter. A portion of the guidewire proximally of the second opening is contained between the catheters, and can be removed from the exterior catheter through a slit running axially along the exterior catheter.