Dr. O'Brien has been in private psychiatric practice since 1987 after he was Board Certified in general psychiatry at the age of 28. He has been performing workers' compensation examinations and has treated industrial injuries since 1989. He was Board Certified in Forensic Psychiatry in 1996. He has performed over seven thousand medical-legal reports in his career including disability evaluations of all types, fit-for-duty examinations, and mental competency assessments. Dr. O'Brien is used nationwide as an expert witness for Defense Base Act evaluations. He is certified in AMA Guides assessment of disability by AADEP. Although he is a psychiatrist, he is an enthusiastic supporter of the use of psychometrics and has frequently lectured on the uses of the MMPI-2 and SIMS. He maintains a private practice in Manhattan Beach, CA.