Introduction: Northwest Africa (NWA) 1500 was classified as an anomalous ureilite [1]. Bartoschewitz et al. [2] described this meteorite as having similarities to typical monomict ureilites, but with significant differences – notably, the presence of plagioclase that might represent the “missing basaltic component” of the ureilite parent body (UPB). They noted, however, that its oxygen isotopic composition is not within the field of ureilites. Mittlefehldt and Hudon [3] considered it to be a unique achondrite. We report an in-depth study of NWA 1500. Petrologically, this meteorite appears to be a ureilite, and one that provides new information about the differentiation of the UPB. Although plagioclase is minor, its presence is highly significant. The oxygen isotopes of this ureilite remain unexplained. Petrography: Three thin sections show that NWA 1500 is an unbrecciated ultramafic rock. Olivine is the most abundant phase (~95%), and shows an equilibrated texture with grain sizes of ~100-500 μm. Augite occurs as a minor phase (2-3%), with grain sizes comparable to or larger (up to ~925 μm) than those of olivine. Many augite grains have intergranular forms (convex boundaries with olivine), and partially enclose olivine grains poikilitically. The presence of augite (and absence of pigeonite) would place NWA 1500 among the small group (<10%) of augite-bearing monomict ureilites [4,5]. Chromite, previously observed only in two monomict ureilites [6-8], is present (0.6-1.6%) with grain sizes up to ~300 μm. Plagioclase (0.7-1.8%) occurs principally as large (up to ~3 mm) poikilitic grains enclosing rounded olivine and augite (Fig. 1) in veinlike areas that also have concentrations of augite and orthopyroxene (opx). It occurs elsewhere as small (~25-150 μm) interstitial grains. Other minor phases are apatite (not previously observed in a monomict ureilite), metal, sulfide and graphite.