Statistical analysis is performed of consistency of the known experimental data on the density of cesium vapor. A semiempirical equation of state with few constants is employed, which is based on “pseudogroup” expansions of pressure and density in powers of activity. The second group integral is theoretically calculated using spectroscopic and quantum-mechanical data on atomic interaction. A modification of this equation of state is suggested, which enables one to approximate experimental data both at low and moderate densities and in the near-critical region. Equations of state are derived, which describe both the data of single experiments and the majority of these data taken together. The experimental data indicative of the significant effect of anomalous ionization of cesium vapor on its thermodynamic behavior are shown to be invalid.