Insulinoma is a rare tumour reported in 10 cases during pregnancy. In most cases, hypoglycaemia occurred during the first trimester and no fetal malformations were noted. We report a new clinical case of insulinoma diagnosed at 6 weeks of amenorrhoea in a 25-year-old woman. Surgery performed at 17 weeks of amenorrhoea confirmed the presence of a 7 mm diameter endocrine tumour in the head of the pancreas and led to a cure. The pregnancy continued without complications, and at 35 weeks the patient gave birth to a 3.5 kg infant with no malformation. This case was investigated in terms of a possible physiopathological cause of insulinoma during pregnancy. There is good evidence that insulin secretion increases rapidly from the beginning of pregnancy because of beta-cell proliferation and enhanced beta-cell sensitivity to glucose stimulus as a result of hormonal changes, i.e., prolactin and/or placental lactogen secretion. Moreover, some studies have suggested that insulin sensitivity is enhanced during early pregnancy. Taken together, these phenomena may explain why insulinoma occurs early during pregnancy. Although repeated hypoglycaemia has caused teratogenic effects in animal models, no fetal malformation has been described in previous reports of insulinoma during pregnancy, whether cured or not. This is in agreement with prospective studies in insulin-treated pregnant diabetic women showing no correlation between hypoglycaemia and malformations. These results are encouraging with respect to such pregnancies which, however, require careful supervision.