3D PbS dendritic nanostructures (see Figure) have been fabricated by a facile hydrothermal method in the presence of N-cetyl-NNN-trimethyl-ammonium. bromide (CTAB). Both CTAB and thiourea play important roles in the formation of well-defined PbS dendrites. X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy results show that the PbS nanostructure is a 3D dendrite of a single crystal.