Photochemical reactions of naphtho[1,2-c][1,2]dithiole-3-thione (7), naphtho[2,1-c][1,2]dithiole-1-thione (10), and naphtho[2,3-c][1,2]dithiole-3-thione (16) with cyclohexene and 2,3-dimethyl-2-butene afford the corresponding naphthothioquinone methides. The thioquinone methide from 7 exists only as a monomeric form and is the first isolable o-thioquinone methide, while that from 16 exists as a dimer of [4+4] type in the solid state although the chemical behavior suggests the presence of a monomeric form in solution to a very minor extent. In the case of the thioquinone methide from 10, there exists an equilibrium between a monomer and a dimer of [4+2] type. Some cycloadditions of these thioquinone methides are also described.