The plasma vertical stability in a single-turn tokamak configuration is analyzed. The stabilization effects of the vacuum vessel and poloidal field magnet are studied numerically with rigid and magnetohydrodynamic models. An analytic mode dispersion relation is derived to estimate the effect of the single-turn toroidal field magnet on the plasma vertical stability. The typical growth time of the mode is found to be >1 s. The stability advantages of the single-turn configuration for a high-current tokamak plasma and the differences among the three models used are discussed. A single-turn tokamak configuration seems to be appropriate for a fusion ignition experiment in that it simplifies plasma control and makes feasible the control of high-current, elongated tokamak ignition plasma.