Communication: Superlattices of self-assembled Ag nanocrystals have been prepared and the structure analyzed using a combination of techniques. It is shown that the supercrystals are hexagonally close-packed, attributed to a high proportion of icosahedral and decahedral particles. The Figure (a TEM image of the Ag supercrystals) illustrates that the crystals formed are predominantly triangular in morphology and can be as large as 3-5 mu m.