The photodissociation dynamics of a water molecule in crystalline ice at 10 K is studied computationally using classical molecular dynamics. Photodissociation in the first bilayer leads mainly to H atoms desorbing (65%), while in the third bilayer trapping of H and OH dominates (51%). The kinetic energy distribution of the desorbing H atoms is much broader than that for the corresponding gas phase photodissociation. The H atoms on average move 11 angstrom before becoming trapped, while OH radicals typically move 2 angstrom. In accordance with experiments a blueshift of the absorption spectrum is obtained relative to gas phase water. (c) 2005 Elseiver B.V. All rights reserved.