This article provides a historical assessment of the role of X-ray therapy in the treatment of bronchial asthma. This analysis revealed that X-ray therapy in the treatment of bronchial asthma spanned the first six decades of the 20th century, and involved nearly 6,000 patients in published clinical case studies. Patients selected typically had at least moderate to severe asthma and were refractory to other commonly employed treatments. The results of more than 60 studies indicated that about 70% of patients had rapid and marked reductions in clinical symptoms with about half of these patients showing complete symptom relief. The duration of the beneficial responses was variable but was approximately 1–6 months for about 50% of the benefited patients, and between 1 to 4 years for the upper 25% of benefited patients. The use of X rays to treat such patients fell into disfavor during the 1950s due to mounting concerns over possible enhanced risks of cancer that coincided with the discoveries and use of antihistamine medications, antibiotics and the methyl xanthine bronchodilators aminophylline and theophylline.