Secreted Frizzled-related protein 2 (Sfrp2) or Stromal Cell Derived Factor-5 (SDF-5) is highly expressed in the developing limbs. Here we showed the single Sfrp2 inactivation in mice resulted in syndactyly and preaxial synpolydactyly, predominantly in the hindlimbs. Tails were often kinked. A penetrance of the syndactyly was highest in 129/SvJ or CBA/N × 129/SvJ background and the phenotype was haploinsufficient. Preaxial synpolydactyly was seen in homozygous mutants in C57BL/6 × 129/SvJ. Of note, syndactyly showed retarded apoptosis of the second and the third interdigital spaces; concomitantly, mesodermal Msx2 expression was down-regulated. Impaired digital anlagen maturation was also noticeable in the same position. Preaxial synpolydactyly of the Sfrp2 mutants was a non-mirror image type and Shh independent. Although joint formation was not disrupted, chondrocyte maturation was preaxially disturbed. Our results suggest that the Sfrp2 deleted mice can be a useful animal model to study human syndactyly/preaxial synpolydactyly defects. Developmental Dynamics 237:2506–2517, 2008. © 2008 Wiley-Liss, Inc.