The synthesis, structure solution, and characterization of the high-silica zeolite SSZ-55 are described. SSZ-55 was synthesized under hydrothermal conditions using a [(1-(3-fluorophenyl)cyclopentyl)methyl]trimethylammonium cation as the structure-directing agent. The framework topology and symmetry of SSZ-55 were determined by the Monte Carlo method ZEFSAII. Rietveld refinement of the X-ray powder diffraction data confirms the space group assignment of Cmc2(1). Transmission electron microscopy confirms the unit cell parameters and the topology of the structure. SSZ-55 contains one-dimensional pores circumscribed by 12 T-atom rings. The topology of SSZ-55 is that of the ATS framework, previously described for AlPO-based molecular sieves.