IR, UV and NMR data reveal that the dichlorination product of 3,5-di-tert-butylphenol is the keto tautomer (1a) of 3,5-di-tert-butyl-2,4-di-chlorophenol (3) instead of the ortho-quinol dichloride (2a), as assumed by Hewitt et al. (1972). According to the crystal structure determination, the first one of a monocyclic keto tautomer, 1a crystallizes in the space group P1̄ with Z = 4; a = 1052.6(3), b = 1202.6(4), c = 1207.4(4) pm, α = 90.52(4)°, β = 95.13(4)° and γ = 108.59(4)°. The structure was solved by direct methods and refined by full-matrix least squares to R = 0.094 for 2176 reflections (I > 3 · δ(I)). Bond lengths and angles show no unusual features; the conformation is discussed with respect to the acidity of the sp3-s CH bond. Suggestions for the mechanism of formation of 1a are presented.