CONTEXT: Insulinomas represent pancreatic neuroendocrine neoplasms (pNEN) that cause severe morbidity attributed to their often pronounced endocrine activity. Apart from hereditary forms such as MEN-1, genetic causes for sporadic insulinoma development had remained obscure until recently. Applying next generation sequencing methods, disease causing genetic alterations have been identified in various endocrine tumors. OBJECTIVE: and Design: Tumor- and matched blood DNA from 8 patients with sporadic insulinomas (5 females and 2 malignant) were analyzed by whole exome sequencing. Following this initial analysis, Ying Yang 1 (YY1) mutation status was assessed in a larger cohort of 39 additional insulinomas (including 8 malignant and 1 liver metastasis) from 3 German hospitals by targeted sequencing. The mutation status was correlated with various clinical parameters. RESULTS: A range of 1 - 12 somatic genetic variants were identified by exome sequencing. A recurrent somatic Thr372Arg YY1 point mutation was detected in 2 patients of the initial and in 4 patients of the second cohort (total 6/47; 13 %). Presence of the mutation was associated with a trend towards higher age (62±13 vs. 48±17; p=0.06) and all affected patients were females (6/6, p=0.04). All other clinical parameters, including presence of malignancy and metastatic spread, tumor localization, and hypoglycemic episodes were not different between YY1 mutated and non-mutated tumor carriers. CONCLUSIONS: The somatic Thr372Arg YY1 mutation is a relevant finding in female patients with sporadic insulinomas. The prevalence of this mutation in this Caucasian population is considerably lower compared to that of a recently described Asian cohort.