SMOC1 and SMOC2 are matricellular proteins thought to influence growth factor signaling, migration, proliferation, and angiogenesis. We examined the expression and regulation of Smoc1 and Smoc2 in fetal gonad/mesonephros complexes to discover possible roles for these genes in gonad and mesonephros development. Smoc1 was upregulated at ∼E10.75 in a center-to-poles wave in pre-Sertoli and pre-granulosa cells and its expression was greatly reduced in Wt1, Sf1, and Fog2 mutants. After E13.5, Smoc1 was downregulated in an anterior-to-posterior wave in granulosa cells but persisted in Sertoli cells, suggesting a sexually dimorphic requirement in supporting cell lineage differentiation. Smoc2 was expressed in Leydig cells, mesonephroi, and Wnt4 mutant ovaries, but not wildtype ovaries. Using organ culture, we determined that Smoc2 expression was dependent on Hedgehog signaling in testes, mesonephroi, and kidneys. Overall, these results demonstrate that SMOC1 and SMOC2 may mediate intercellular signaling and cell type–specific differentiation during gonad and reproductive tract development. Developmental Dynamics 238:2877–2890, 2009. © 2009 Wiley-Liss, Inc.