We calculate the cosmic microwave background ( CMB ) bispectrum due to inhomogeneous reionization .
We calculate all the terms that can contribute to the bispectrum that are products of first order terms on all scales in conformal Newtonian gauge .
We also correctly account for the de-correlation between the matter density and initial conditions using perturbation theory up to third order .
We find that the bispectrum is of local type as expected .
For a reasonable model of reionization , in which the universe is completely ionized by redshift z _ { ri } \sim 8 with optical depth to the last scattering surface \tau _ { 0 } = 0.087 the signal-to-noise ratio for detection of the CMB temperature bispectrum is S / N \sim 0.1 and confusion in the estimation of primordial non-Gaussianity is f _ { NL } \sim - 0.1 .
For an extreme model with z _ { ri } \sim 12.5 and \tau _ { 0 } = 0.14 we get S / N \sim 0.5 and f _ { NL } \sim - 0.2 .