Nesidioblastosis is an exceedingly rare occurrence in the adult and, when it appears, it is usually part of a MEA1 syndrome. We present a case of nesidioblastosis in a young woman, with no concurrent endocrine pathology, while we discuss in detail the diagnostic and therapeutic problems posed by this condition. The selected treatment was sub-total pancreatectomy (70-80%) and the histopathologic and immunohistochemical tests of the surgical specimen showed: "Diffuse Nesidioblastosis". The histopathologic and immuno-histochemical features of the resected pancreas are analysed in detail.