We have used a variational procedure within the envelope-function and parabolic-band approximations to investigate the effects of hydrostatic pressure and crossed electric and magnetic fields on shallow-donor states in GaAs/Ga1-xAlxAs quantum wells. The donor variational envelope wave function is obtained through a hydrogenic 1s-like wave function and an expansion in a complete set of trigonometrical functions, and a detailed study is performed of the dependence of the donor binding energies on the applied hydrostatic pressure and applied in-growth direction electric and in-plane magnetic fields.