In adults, celiac disease (CD) diagnosis is based on specific serology (anti-transglutaminase IgA-anti-tTG) and duodenal histology. Evidence is raising the possibility of perform CD diagnosis based only on high anti-tTG titer in children. We aimed to evaluate clinical, histological and biochemical differences between adult patients with high tTG IgA titer (HT) and those with low titer (LT) at CD diagnosis and follow-up. This retrospective study included consecutive adult CD patients divided into two groups: HT (anti-tTG > 10 × ULN) and LT (anti-tTG < 10 × ULN). Clinical, biochemical and histological features were compared between groups at CD diagnosis and at follow-up. A total of 291 patients were included (HT: 47.1%; LT: 52.9%). At CD diagnosis, HT patients showed a non ‘classical’ presentation (p= 0.04), Marsh 3C (p= 0.005), hypoferritinaemia (p= 0.006) and osteopenia/osteoporosis (p= 0.04) more frequently than LT patients. A total of 216 patients (HT: 48.6%; LT: 51.4%) performed a follow-up after a median Gluten-free diet of 14 months; HT patients had persistent antibodies positivity (p= 0.001) more frequently and GI symptoms (p= 0.04) less frequently than LT patients. In conclusion, HT patients presented severe histological damage more frequently at diagnosis, recovering similarly to LT patients after the start of the Gluten-free diet. At follow-up, anti-tTG persisted positive in HT more frequently compared to LT patients, without differences regarding histological recovery and clinical improvement.