  We investigate the photometric redshift distribution, colours and
morphologies of a large sample of submillimetre sources in the GOODS-North
region. With the depth achieved by the deep ACS images, optical counterparts
have been found for all the radio-detected sub-mm sources, and we have used
several techniques to identify counterparts to the radio-undetected sources.
The sub-mm counterparts have a median photometric redshift, from optical and
near-IR photometry, of 1.9. Our sample contains a much higher fraction of EROs
than other sub-mm surveys, and larger angular sizes than the average galaxy at
all redshifts. The sub-mm galaxy counterparts are consistent with massive
star-forming galaxies at high redshift.
