Hereditary angioedema (HAE) is characterized by nonpitting, nonpruritic subcutaneous, or submucosal edema that may be accompanied by a nonpruritic serpentine erythematous rash. The swelling in this autosomal dominantly inherited disorder is mediated by uncontrolled localized bradykinin production. The extremities, face, gastrointestinal tract, genitalia, larynx, and trunk are commonly involved. Nearly one-third of patients who are not treated may suffer asphyxiation from a laryngeal attack. HAE symptoms overlap with other conditions that cause swelling. An accurate diagnosis is therefore crucial when considering therapy. Recently approved treatments for HAE swelling attacks include C1 esterase inhibitor concentrate and ecallantide. This case describes a 41-year-old woman who was treated ineffectively for more than 20 years, was switched to an effective therapy, but suffered near fatal laryngeal edema due to a missed dose of the effective therapy. The case underscores the need for increased awareness of HAE among clinicians and the importance of good compliance to therapy among patients with HAE.