In a method and apparatus for mechanically fastening a partially assembled absorbent undergarment during manufacture, a longitudinal folding device is carried by a transport device and moveable between an open configuration in which it receives a partially assembled undergarment, and a closed configuration in which the undergarment is folded longitudinally by the folding device. A first transverse folding device folds a first fastening portion of the undergarment relative to the folding device and generally toward a second fastening portion, and a second transverse folding device carried by the transport device folds the second fastening portion relative to the folding device and generally toward the first fastening portion to facilitate engagement therebetween. A separate retention member is carried by the transport device and draws at least one of the first and second fastening portions against the retention member while the garment is moved by the transport device.