Modern Cannondale bikes feature the bicycle's serial number on the underside of the frame:

Location of the bar-coded serial number sticker
The bicycle's serial number will be accompanied by a bar code:

Serial Number
Once you have located your serial number you can register your bike directly through the link below:
Vintage and older Cannondale bikes may have serial numbers placed on other areas of the frame. For a list of other locations, please click the link below: