Cognitive remediation therapy (CRT) is a low-intensity treatment adjunct for individuals with severe and complex anorexia nervosa (AN) with difficulties in globally oriented, flexible thinking. Previously trialled in adults, this study investigated whether individual and group CRT was a feasible, acceptable, and beneficial treatment for 125 adolescent inpatients with severe and complex AN. Seventy patients (mean age = 15.22, SD = 1.44) received 10 sessions of individual CRT, and 55 patients (mean age = 14.89, SD = 1.74) received 10 sessions of group CRT. In individual CRT, 1 patient (1.43%) dropped out, and there were medium-sized improvements in bigger picture thinking and set-shifting, small to large-sized improvements in switching-related initiation and inhibition skills, and large-sized improvements in motivation to recover. Group CRT had higher dropout (9.09%; n = 5) and produced small-sized improvements in global information processing and medium-sized improvements in self-reported cognitive flexibility and high acceptability ratings. Data suggest that a randomised controlled trial for adolescents with AN is warranted.