Purpose <p>This study aimed to investigate the usefulness of ultrasound-guided core-needle biopsy (US-CNB) for diagnosing type 1 AIP and evaluate the radiological outcomes following steroid therapy.</p> Materials and Methods <p>From January 2017 to June 2023, patients with pathology results containing “lymphoplasmacytic infiltration” and “fibrosis” were enrolled. The detection rate of level 1 histology by International Consensus Diagnostic Criteria (ICDC) and the contribution of US-CNB were assessed. The radiological responses to steroid therapy following biopsy were assessed and classified.</p> Results <p>Sixty-one patients were included, 56 of whom ended up with a diagnosis of type 1 AIP. Twenty-six (46.4%, 26/56) patients met the level 1 criteria of type 1 AIP. Of the 61 enrolled patients, 27 (44.3%) were diagnosed with definitive type 1 AIP without evidence from histology. The addition of pathologic evaluation of the pancreas tissue collected by US-CNB improved the diagnostic rate of definitive type 1 AIP to 67.2% (44.3% vs. 67.2%, p = 0.017). Among the remaining 20 undiagnosed patients, 13 (21.3%) finally were diagnosed with definitive type 1 AIP, and 2 (3.3%) with probable type 1 AIP by a diagnostic steroid trial (67.2% vs. 91.8%, p = 0.001). At the 12-month follow-up, a favorable response was observed in 48 patients, a partial response in 5 patients, relapse in 1 patient and disease progression in 2 patients.</p> Conclusion <p>US-CNB is an effective diagnostic method for type 1 AIP. A high remission rate of AIP was achieved with the addition of US-CNB to the diagnostic algorithm.</p> Graphical Abstract <p></p>