The diagnosis of food allergy depends on thorough medical history-taking that may be supplemented with trials of dietary eliminations, skin testing, and specific IgE antibody measurement. However, the reliability of such procedures is often suboptimal. For most cases, oral challenge testing is needed to confirm the diagnosis of food allergy and to identify the causative food(s). Though blinded challenges are ideal, open challenges can be appropriate in some cases, particularly in young children. An optimal design of the procedure would depend on the age of the patient, the anticipated symptoms, and the provoking food quantity. The test is much safer than many surgical and medical procedures being routinely performed. This article presents a practical guideline that can reliably and safely encourage an increased use of this important test in the diagnosis of food allergy.