Dr. Thomesen was appointed the Chief of Staff in October 2019.  Dr. Thomesen graduated from Mount Sinai School of Medicine and completed a residency in Psychiatry at LIJ Medical Center.  Dr. Thomesen served as Acting Chief, Psychiatry Service in Northport and officially became Chief of Psychiatry/ACOS Mental Health in 1998.

Dr. Thomesen is a member of the Mental Health Executive Board – VISN 2, The VISN 2 Suicide Prevention Workgroup, Mental Health Council-chair, Crisis Prevention Committee-chair, Patient Care Review Committee and the Professional Standards Board.

Dr. Thomesen is Board Certified by the American Board of Psychiatry and Neurology in Adult Psychiatry with Subspecialty Board Certification in Forensic Psychiatry.