Intensive treatment regimens including early initiation of insulin treatment are important to prevent late complications in type 2 diabetes. The assumed risk of severe hypoglycemia (SH) is a major barrier to initiation of insulin treatment. To assess the relevance of this risk we evaluated the frequency of SH as reported in the literature. Using Medline and Embase search we identified 11 studies (5 retrospective and 6 prospective) including at least 50 patients with insulin-treated type 2 diabetes followed for at least 6 months in which frequency of SH was reported. The incidence of SH in the retrospective studies varied from 15 to 73 episodes per 100 patient-year with a proportion of the patients having one or more episodes between 1.4 to 15%. In the prospective studies, both incidence rate and proportion of the patients having one or more episodes of SH were lower than in the retrospective studies. Only few studies looked into the impact of risk factors on the rate of SH. Impaired hypoglycemia awareness, high age, long duration of diabetes and insulin therapy increased the risk, while no association was found with HbA1c and insulin dose. The present knowledge of SH in insulin-treated type 2 diabetes is characterized by the paucity of data and the heterogeneity of the few studies available. Large and long-lasting studies with SH as primary endpoint are warranted in order to further clarify the occurrence of SH and influence of the risk factors in unselected patients with insulin-treated type 2 diabetes.