Photolysis of dimethyl sulfoxide in a molecular beam with 210 and 222 nm photons reveals the decomposition mechanism and energy disposal in the products. Using vacuum ultraviolet light and a time-of-flight spectrometer, we identify CH3 and CH3SO as primary fragments and CH3 and SO as secondary fragments. From CH3 quantum yield measurements, we find that secondary decomposition is minor for 222 nm photolysis, occurring in only about 10% of the fragments, but it increases to about 30% in the 210 nm photolysis. Laser-induced fluorescence measurements on the B(3)Sigma(-) <-- X(3)Sigma(-) transition of SO in the 235 to 280 nm region determine the internal energy of that photoproduct. We compare our results to a simple statistical model that captures the essential features of the decomposition, predicting both the extent of secondary decomposition and the recoil energy of the primary and secondary methyl fragments.