Reactive hypoglycemia is a relatively uncommon meal-induced hypoglycemic disorder. Most patients with adrenergic-mediated symptoms have a diagnosis other than reactive hypoglycemia. In many patients with this self-diagnosis, other disorders can be attributed as a cause for symptoms, especially neuropsychiatric disease. The continued use of the terminology "functional hypoglycemia" only contributes vagueness to our correct understanding of this metabolic condition. There are a number of conditions associated with postprandial hypoglycemia. One category is the reactive hypoglycemias, which occur in patients with diabetes mellitus (diabetes reactive hypoglycemia), gastrointestinal dysfunction (alimentary reactive hypoglycemia), hormonal deficiency states (hormonal reactive hypoglycemia), and a large patient group characterized as having idiopathic reactive hypoglycemia. Of these causes the alimentary, hormonal, and diabetic patients are less disputed, whereas the idiopathic reactive hypoglycemic group has been referred to as a "nondisease" group. Characteristic alterations in insulin secretion accompany each of these conditions. In bona fide patients, dysinsulinism or hyperinsulinism usually accounts for the hypoglycemia. Some patients may have increased insulin sensitivity, but this association is doubtful or very rare. Patients with this meal-related eating disorder are characterized as ingesting excessive quantities of refined carbohydrate. In the research setting, the disorder can easily be elicited with the oral glucose tolerance test. However, to establish clinical relevance, the hypoglycemia needs documentation in the home setting with measurements of blood glucose during a postpradial symptomatic episode. The reactive hypoglycemic patients are frequently confused with patients with underlying psychiatric illness. Both syndromes are similar, with adrenergic-mediated symptoms and a common characteristic personality as noted on Minnesota Multiphasic Personality Inventory (MMPI) testing. Patients with bona fide meal-related reactive hypoglycemia should be treated primarily with dietary restriction of refined carbohydrates; other patients may require medications.