We have grown epitaxial NiMnSb(001) films on GaAs(001). NiMnSb is a half-metallic ferromagnet and a possible candidate for spin injection applications. Films grown at a Sb:Ni flux ratio φ S b :φ N i =7:1 have the best crystal quality and surface morphology, but show a Mn deficiency of ~20at% and a reduced magnetization. Stoichiometric films show the highest magnetization and are obtained at φ S b :φ N i =10:1. The implication of the twofold in-plane magnetic anisotropy, dependent on the growth conditions, on the interface structure and the spin polarization at the bottom NiMnSb surface will need further attention.