We study diffusion of self-interstitial atoms (SIAs) in vanadium via molecular-dynamics simulations. The 〈111〉-split interstitials are observed to diffuse one-dimensionally at low temperature, but rotate into other 〈111〉 directions as the temperature is increased. The SIA diffusion is highly non-Arrhenius. At T < 600 K, this behavior arises from temperature-dependent correlations. At T > 600 K, the Arrhenius expression for thermally activated diffusion breaks down when the migration barriers become small compared to the thermal energy. This leads to Arrhenius diffusion kinetics at low T and diffusivity proportional to temperature at high T.