We extend the work of Mitchell et al., on the decay of highly excited open strings, to closed strings. We use the optical theorem, plus an expansion in level number of the final states, which allows the subtraction of tachyonic processes. Computer results in 26 dimensions, for initial states of level number N up to 70, suggest an asymptotic form of N−12 for the total decay rate. We also consider the truncated theory in d = 4, for comparison with cosmic string calculations of gravity wave emission, and find that massless particle processes dominate in this case. We calculate these processes analytically, leading to an asymptotic decay rate proportional to N−12.