The absorption spectrum of thioacetone, (CH 3) 2CS, has been surveyed over the region 700-190 nm, and five distinct absorptions have been identified. These are the spin-allowed and spin-forbidden n → π ∗, Ã( 1A 2) ← X∼( 1A 1) , and ã( 3A 2) ← X∼( 1A 1) transitions; the orbitally allowed π → π ∗, B∼( 1A 1) ← X∼( 1A 1) transition; and the Rydberg transitions n → 4 s, C∼( 1B 2) ← X∼( 1A 1) , n → 4 pz, D∼( 1B 2) ← X∼( 1A 1) , and n → 4 py, Ẽ( 1A 1) ← X∼( 1A 1) . In addition, the laser phosphorescence excitation spectrum has been obtained for the ã ← X∼ transition. Partial vibrational assignments have been obtained for all of the excited electronic states. The analyses showed that the ã, Ã, and C∼ states are all planar or pseudo-planar. Of interest is the vibrational activity of the methyl torsional modes. The presence of torsional progressions in the visible absorption spectrum led to the conclusion that the CH 3 groups are rotated in the ã state by 60° from the X∼ state. Observation of torsional sequence transitions rather than progressions in the C∼ ← X∼ spectrum indicates that the methyl groups do not change their configuration on excitation into the C∼ state.