Catocala piatrix, the penitent underwing, is a moth from North America.

The forewings are dark brownish gray, darkest at the base, and with an oblique lighter band extending from the midwing to the leading edge near the wing base.

The hindwings are yellow orange with dark hairs at the base (though these are not especially prominent) and two concentric black bands.

The yellow zone separating the black bands is wide, with a relatively smooth edge; the outer edge of the hindwings is light yellow with some black bars extending from the outer band.

The larvae feed on ash, butternut, hickory, pecan, persimmon, and walnut trees.