San Antonio-born, Dr. Diaz followed in his father's footsteps, Jose A. Diaz, M.D., family practitioner, who had a successful medical practice on the south side of San Antonio for 30 years. 

Dr. Diaz graduated from St. Mary's University in San Antonio, with high honors and a B.S. in Biology. He received his medical degree from the University of Texas Medical Branch at Galveston, Texas. His internship and residency, as well as his fellowship in Allergy and Immunology, was completed at the University of South Florida College of Medicine. Since opening his private practice, Allergy, Asthma and Immunology Associates of South Texas in 1988, Dr. Diaz has served as clinical assistant professor in the Department of Internal Medicine at the University of Texas Health Science Center in San Antonio. He was appointed Co-Director of the Allergy/Clinic Immunology Fellowship training program and directed the program for several years.

In addition to his private practice, Dr. Diaz is the President and Medical Director of Allergy and Asthma Research Center, established in 1989. As Medical Director of the Research Center, Dr. Diaz says his patients benefit from access to new medicines and information not yet available to most physicians or patients. In Dr. Diaz' free time, he enjoys physical fitness, competing in Iron Man competitions and spending time with family.