Ferroelectric nanostructures have been fabricated by self-assembly, using the high temperature instability of ultra thin films. Lead zirconate titatnate (PZT) structures, as small as 20 nm lateral size with a height of 9 nm, have been fabricated on (100) SrTiO3 substrates. The shapes and sizes of the ferroelectric structures could be tuned within a small range by varying the initial thickness of the as deposited film and crystallisation annealing. Introduction of intentional defect sites prior to the crystallisation treatment had a pronounced effect on the shape and size of the final nanostructures. The ferroelectric switching of individual nanoislands of 50 nm lateral size and 25 nm height islands was shown by piezoresponse AFM.