With acaulescent hybrids - like Helleborus x hybridus (aka orientalis hybrids) - removal of last year's growth is a standard practice. By late winter the foliage is likely limp, often splaying to the ground, and typically battered by weather and diseases. Removal of the foliage in late winter - just as the flower buds are emerging from the ground - certainly does not weaken the plan and can actually improve vigor by removing overwintering fungal spores and various insect pests. New foliar growth is almost immediate and the flowers are displayed to much better effect with the removal of old growth.

With the caulescent species and hybrids, this practice is very optional. These tend to produce much more upright and durable foliage and also much more attractive foliage. Typically one only needs to remove any badly disfigured foliage or any that is obviously dried up or dead. Even evergreen foliage doesn't last forever :-))

This year a grower near you (SEPa) told me he cuts his back just before autumn leaves drop, in order to make fall cleanup easier. Says the earlier trim doesn't effect vigor at all and if I had a big woodland planting I would definitely consider this.
Like Gal said, trimming in spring is standard practice.

kato_b

That sounds interesting. I might think about it for next fall. This year has really been horrible down here with snow/thaw cycles beyond belief.

Still, the hellebores are gorgeous this spring. Have had bloom starting about 2 weeks ago on the hybridus and a month or more on niger. Foetidus is even starting although the winter burnt off a lot of those buds. First year blooming on a lot of niger seedlings, which I spread around last year as well as a good number of hybrids seedlings.

If the foliage looks like crap, I prune it. If it looks good, I leave it.