A boy affected by severe obesity (kg 117, Body Mass Index 37 kg/m2) and acanthosis nigricans, was treated with octreotide for 150 days (50 micrograms x three daily subcutaneous administrations). Before treatment the patient showed an exaggerated insulin (IRI) and C-peptide (CPR) response to a standard meal with a lowering in after-meal CPR/IRI molar ratio. During octreotide treatment both IRI and CPR response was reduced but CPR/IRI molar ratio rised after meal indicating an increase in hepatic insulin removal. Body weight and acanthosis nigricans were sharply reduced during treatment and the reduction was still maintained six months after the cessation of therapy. Furthermore, IRI and CPR response, as well as the behaviour of CPR/IRI molar ratio, remained within normal range. In conclusion long-term octreotide treatment has been able to correct hyperinsulinemia and to reduce body weight and acanthosis nigricans.