Full dimensional wave packet calculations are performed to model the unimolecular dissociation HCO --> H + CO on its ground electronic state. Results of calculations up to total (nuclear) angular momentum J = 10 are reported. Most of our results are based on the recent potential surface of Werner, Keller, Schinke, and co-workers, although some comparative results with the earlier surface of Bowman, Bittman, and Harding are also presented. We focus on certain unimolecular resonances, and determine their positions, widths, and associated CO product distributions. We find good agreement with the available experimental results of Neyer et al. We also consider how rotation affects a group of states associated with the 2:1 stretch/bend resonance. Bowman's adiabatic rotation model is found to provide a reasonable description of our results, and is also a useful tool for analysis. (C) 1997 American Institute of Physics.