  We derive a dispersion relation for the S parameter in the SO(5)/SO(4)
Minimal Composite Higgs model. This generalizes the Peskin-Takeuchi formula to
the case when a light Higgs boson is present in the spectrum. Our result
combines an IR effect due to the reduction in the Higgs boson couplings with a
UV contribution from the strong sector. It also includes a finite matching
term, achieving a very good relative accuracy O(m_h/m_\rho). We apply our
formula in several toy examples, modeling the UV spectral density via Vector
Meson Dominance.
