AbstractBackground The limited data on the utility of endoscopic ultrasound (EUS)-guided through-the-needle biopsies (TTNBs) in patients with pancreatic cystic lesions (PCLs) originate mainly from retrospective studies. Our aim was to determine the clinical impact of TTNBs, their added diagnostic value, and the adverse event rate in a prospective setting.Methods This was a prospective, single-center, open-label controlled study. Between February 2018 and August 2019, consecutive patients presenting with a PCL of 15 mm or more and referred for EUS were included. Primary outcome was a change in clinical management of PCLs following TTNB compared with cross-sectional imaging and cytology. Adverse events were defined according to the ASGE lexicon.Results 101 patients were included. TTNBs led to a change in clinical management in 11.9 % of cases (n = 12). Of these, 10 had serous cysts and surveillance was discontinued, while one of the remaining two cases underwent surgery following diagnosis of a mucinous cystic neoplasm. The diagnostic yield of TTNBs for a specific cyst diagnosis was higher compared with FNA cytology (69.3 % vs. 20.8 %, respectively; P < 0.001). The adverse event rate was 9.9 % (n = 10; 95 % confidence interval 5.4 % – 17.3 %), with the most common event being acute pancreatitis (n = 9). Four of the observed adverse events were severe, including one fatal outcome.Conclusions TTNBs resulted in a change of clinical management in about one in every 10 patients; however, the associated adverse event risk was substantial. Further studies are warranted to elucidate in which subgroups of patients the clinical benefit outweighs the risks.