The synthesis of nanocrystalline PbS quantum dots using organometallic precursors is reported. The samples exhibit tunable, strong near-infrared photoluminescence. A remarkable spontaneous self-directed narrowing of the particle sized distribution is shown to occur after the particles are synthesized and dispersed in organic solvent. The Figure shows the tuning of band-edge exciton absorption features through the near-infrared spectral region according to particle size.