The short distance behavior of massive integrable quantum field theories is analyzed in terms of the form factor approach. We show that the on-shell dynamics is compatible with different definitions of the stress-energy tensor T(munu)(x) of the theory. In terms of form factors, this is equivalent to having a possible nonzero matrix element F1 of the trace of T(munu) on a one-particle state. Each choice of F1 induces a different scaling behavior of the massive theory in the ultraviolet limit.
