Abstract: The thermal expansion tensor of crocoite has been determined from high-resolution neutron time-of-flight powder diffraction data. The temperature dependence of the lattice constants between 4.5 K and 290 K have been fitted to a quasi-harmonic Einstein model, and the temperature dependence of the thermal expansion tensor has been calculated for 60 K ≤ T ≤ 290 K. The magnitudes of the principal expansivities and their orientation exhibit saturation behaviour for temperatures above 300 K. The predicted saturated expansion coefficients are α₁₁ = 33.1(1) × 10⁻⁶K⁻¹, α₂₂ = 15.72(3) × 10⁻⁶K⁻¹, α₃₃ = 3.36(1) × 10⁻⁶K⁻¹, with α₂₂ parallel to b and α₁₁ lying at an angle of −37.86(5)° to c for the P2₁/n setting of the crystal structure. The direction of maximum expansion is approximately parallel to both [101¯] and the least-squares line passing through the projection of the chromium atoms on (010). The direction of minimum expansion lies approximately parallel to [101]. No evidence was found for either a structural or magnetic phase transition between 4.5 K and 300 K.