A first-principles computation of tetragonal distortion, structural stability, and equation of state has been carried out for indium, using the linear muffin-tin orbital electron-band-theory technique. Results on the variation of tetragonal distortion (c/a) with compression show a broad maximum around V/V 0 ≅ 0.8 (19 GPa) in agreement with experimental data. We do not find 5s5p-to-5d electron transfer as speculated to be the cause of the maximum in c/a. However, our results reveal that the core overlap resulting from broadening of the 4d states is the probable reason for the turnover in the c/a ratio. Within the atomic-sphere approximation we find the face-centered orthorhombic phase to be marginally stable beyond 56 GPa in accord with the experiments of Takemura et al.