This article describes an investigation of diesel sprays using multiple-wavelength extinction to probe the region of high droplet number density surrounding the injector tip. Multiple-wavelength extinction used lasers at 9.2 and 0.633 mu m coaligned and focused into a 0.25 mm beam as it traversed the spray. The diagnostic technique is discussed in detail, along with the effect of size distributions on the measurement. Droplet sizes for a room-ambient system, high-pressure and room-temperature system, and a combusting spray system are presented. For the room-ambient sprays, the droplet diameters were typically between 5 and 8 mu m for locations 5, 10, 15, and 25 mm from the injector tip. The behavior of the high-temperature combusting spray was markedly different than its room-temperature counterpart as little as 10 mm from the injector tip. High-temperature fuel sprays displayed all initial period with steady droplet number densities followed try an apparent ignition and subsequent significant temporal variation in number density. Droplet diameters were observed to be near 3.5 mu m for the combusting system. Comparisons of these results with predictions based on published correlations for primary and secondary breakup are also presented.