This paper reviews size effects in nanocrystalline metals and alloys made by electroforming, a particular form of electrodeposition. The main size effects in these fully dense, three-dimensional nanomaterials come from grain size reduction to less than 5 nm and down towards the limit of the amorphous structure. Details will be given on the synthesis of such materials and their microstructural characteristics including reduced crystal size and intercrystalline defect density. Properties which show either weak or strong grain size dependence will be discussed and compared with the structure-sensitivity of various properties in conventional polycrystalline materials.