The effects of Cs adsorption on a TiN_0.83(100) surface have been investigated. Both work-function changes and XPS-derived coverage data show behaviour typical for Cs overlayers on metallic substrates. The intensity and binding energy of a surface-localised Gamma Tamm state relative to the TiN valence band, as monitored by ARPES, do not change with coverage. This is in contrast to the effect of Cs on the (100) surface states of W, Mo and Ta. The authors believe this behaviour can still be explained using the theoretical models for the latter systems by considering the nature of the TiN Tamm state.