Photochemistry in HI cluster species, generated in a seeded supersonic expansion, was initiated by laser excitation into the first UV continuum and probed by photoionization within the same laser pulse. Only one new product species was detected, I-2(+), but the HI+, H+, and I+ signals all show the effects of cluster formation. The I-2 product is formed in the neutral complex through a two-photon process rather than a single-photon event. The laser intensity dependence of the HI+ and I+ signals increases due to new mechanisms of production that become active in the duster. The HI+ wavelength spectrum is perturbed, but no ions of the type (HI)(n)(+) are detected, possibly due to a large geometry change subsequent to ionization which results in rapid fragmentation. Our studies constitute the first detailed probes of photochemistry occurring in hydrogen halide clusters.