We investigate the possibility of a vortex-glass transition in a disordered type-II superconductor in a magnetic field in three dimensions by numerical studies of a simplified model. Monte Carlo simulations at finite temperature and domain-wall renormalization-group calculations at T=0 indicate that d=3 is just above the lower critical dimension dl, though the possibility that dl=3 cannot be definitely ruled out. A comparison is made with XY and Ising spin glasses. The (effective) correlation-length exponent ν and dynamical exponent z are in fairly good agreement with experiment. © 1991 The American Physical Society.