Approximately 30% of patients hospitalised with severe ulcerative colitis do not respond to corticosteroids, but the decision to introduce salvage therapy is delayed to at least the third day of treatment, according to the widely applied Oxford criteria to assess response. This pilot study aimed to determine if gastrointestinal ultrasound performed on admission can predict steroid-refractory disease. In 10 consecutive patients with severe ulcerative colitis, gastrointestinal ultrasound was performed within 24 h of admission. Six patients failed corticosteroids and required infliximab salvage therapy. Colonic bowel wall thickness was a median of 4.6 mm (range 4.2-5.6 mm) in those responding to steroids compared with 6.2 mm (6-7.9 mm) in those requiring salvage therapy (p = 0.009). Any colonic segment with a bowel wall thickness of >6 mm was associated with the need for salvage therapy (p = 0.033). Gastrointestinal ultrasound may provide an early indication of poor corticosteroid response and enable a timelier introduction of salvage therapy in patients with severe ulcerative colitis.