The by-catch of witch flounder (Glyptocephalus cynoglossus) was studied in the Spanish deep-sea fishery for Greenland halibut, which developed in the NAFO Regulatory Area in Div. 3LMNO over the period 1991–94. A total of 32 483 hauls were sampled. Some data from the Div. 3NO Spanish bottom trawl survey in 1995 and 1996 were also included in this study. Witch flounder yield was estimated for this period. The yield showed an annual seasonality where yield was greater in spring. Through the period 1992–96, the overall annual yield showed a general increase. The length frequency and the length/weight relationship were obtained from samplings performed at depths ranging from 800 m to 1500 m. The length range of the individuals was 26–60 cm in males and 22–72 cm in females. The mean length decreased throughout the period analyzed, and was higher in the large vessel catches. The individuals were also larger in Div. 3M. The sex ratio showed seasonal variation in the large vessel catches, while no clear trend appeared in the small vessels. In addition to Greenland halibut, which was the target species, the main fish species accompanying the witch flounder catches were redfish, grenadiers, skate and American plaice as incidental catch.