We have measured accurate x-ray crystallographic data from the InSb(111)2×2 reconstructed surface using synchrotron radiation from the DORIS storage ring at DESY. We have analyzed these independently of all models and find a structure with seven atoms in the unit cell, implying that one site is unoccupied. The bonding configuration is reasonable for a III-V semiconductor surface, and is topologically identical (in projection) to the "vacancy-buckling" model proposed for the GaAs (111)2×2 surface. The differences between the InSb and GaAs structures are significant and reflect chemical trends in the periodic table. © 1985 The American Physical Society.