J. Brennan Cassidy


J. Brennan Cassidy

Primary Specialty:  Doctor of Medicine
Experience: 38 + Years
Medical Education: Doctor of Medicine from the University of Louisville, Kentucky
Stereotactic Radiosurgery, Glioma

Bachelor of Science with a Major in Biology (Pre-Medical) from Xavier University, Cincinnati, Ohio.

Minor in Chemistry and Philosophy from Xavier University, Cincinnati, Ohio.


Dr. Brennan Cassidy is a board-certified family practitioner in Newport Beach, California. 


Dr. Cassidy is highly regarded as one of Orange County’s leading board-certified family medicine and emergency medicine practitioners and for his contributions to the profession, he was named Physician of the Year in 2004 by the Orange County Medical Association. 


Dr. Cassidy also enjoyed a distinguished tour as an active-duty flight surgeon in the United States (US) Navy from which, having faithfully and patriotically performed your duties, earned an honorable discharge. His military service was recognized with a personal achievement citation for outstanding service to the United States awarded by the Commanding General of the US Air Force – Pacific. 


Dr. Cassidy earned a Bachelor of Science with a Major in Biology (Pre-Medical) and Minor in Chemistry and Philosophy from Xavier University, Cincinnati, Ohio. He earned a Doctor of Medicine from the University of Louisville, Louisville, Kentucky where he was Medical School Student Body President, Student American Medical Association Chapter President, and Midwest Regional Secretary. Brennan completed his training at the University of California, Irvine, Orange County Medical Center.


Over the years, Dr. Cassidy has held leadership roles on the medical staff at Hoag Memorial Hospital Presbyterian, Newport Beach, California (Hoag Hospital), where he is currently on the affiliate medical staff in the Department of Community Medicine. Additionally, Brennan has served as the chair or vice- chair of the following Hoag Hospital departments, groups, and committees: Family Medicine, Physicians Emergency Care Medical Group, Paramedic Advisory Committee, Emergency Room Committee, Department of Emergency Medicine.


In addition to being the former Medical Director of the Hoag Hospital Emergency Department, Dr. Cassidy was the founding chair of the Newport Primary Care Medical Group and a founding member of the board of directors of the Coastal Physicians Purchasing Group.


Dr. Cassidy is an expert on workers’ compensation utilization review and peer review having done over one thousand reviews and audits for Comp Partners, Inc. of Irvine, California and over seven thousand reviews for Health Direct/OEHN, Inc. of Dallas, Texas.


Dr. Cassidy’s community service to Orange County includes serving as a member of the Sheriff’s Advisory Council since 1985 and as a Sheriff Department Level III Reserve Sergeant from 2000-2014. 

A past president of the Orange County Medical Association (1999-2000), Dr. Cassidy also served as president of the California Medical Association (2009-2010) and chaired its board of trustees (2005-2008). 

Dr. Cassidy brings to the Ostentus Advisory Board extensive family practice and emergency medicine practice expertise and a track record of leadership in the medical profession in the State of California that will be an asset to the team at Ostentus.