Pant type nappies, or diapers, are provided with lateral tabs applied by a device comprising a conveyor (10) on which absorbent central bodies (3), one per nappy (2), are caused to advance in succession along a given feed direction (D), also a feed device (12) facing the conveyor (10) and supplying a succession of prefolded lateral tabs (4), ordered in pairs. A pair of tabs (4) is placed on each absorbent central body (3) in turn, and at least a first end (4a) of each tab (4) fixed to one corresponding edge of the body. The device further comprises a folding mechanism operating along the conveyor (10), downstream of the feed device (12), by which the successive absorbent central bodies (3) are bent double, and respective second ends (4b) of the two lateral tabs (4) fastened to the edges of the body (3).