My mission is to treat my patients with compassion and kindness and take the time to know and understand them.

I am certified by the American Board of Internal Medicine in Internal Medicine, Medical Oncology and Hematology. I received my BA in Biology at State University of New York at Buffalo and my MD from Jefferson Medical College of Thomas Jefferson University in Philadelphia, PA. I did my residency in Medicine at Lankenau Hospital in Philadelphia, PA and Fellowship in Hematology-Oncology at University of Connecticut Health Center in Farmington, CT. I was recognized in Boston Magazine's 2017 Top Doctors list. Outside of work, I enjoy listening to classical music, traveling, running, and bicycling. 

I grew up in southern Maine and attended Harvard University for my undergraduate education. While at Tufts University School of Medicine and Mount Auburn Hospital in Cambridge, my focus was on primary care medicine. I believe in the dignity of each of my patients. Respect, compassion, and reliability are among my goals in patient care. In my free time, I enjoy the outdoors and the arts, usually in the company of my family. 

As the Medical Director of Addiction Medicine at South Shore Health, I work to tackle the defining medical challenge of our time: Substance use and alcohol use disorder.

In addition to seeing adult patients at South Shore Hospital, I work with colleagues across South Shore Health to develop and implement a comprehensive addiction medicine treatment program. This program will connect patients with the resources they need to manage substance use disorder, no matter if they come to us through the Emergency Department, primary care, or another setting. Additionally, I serve as Medical Director for Spectrum Health System's opioid treatment program, ATS/detox, CSS, and therapeutic community in Weymouth.

Prior to my work at South Shore Health, I helped launch the Bridge Clinic at Boston Medical Center, which connected patients with treatment options for substance use disorder. I also served as Medical Director for Spectrum Health Systems’ Opioid Treatment Program in Weymouth.

In my spare time, I enjoy baseball, reading fiction, snowboarding, and cooking.

It is a privilege to help people,and manage and coordinate exceptional patient care in the hospital. I believe that everyone's medical care should be individually tailored. We all have unique characteristics that need to be considered when deciding a treatment plan. Communication is paramount. Outside of work, I love reading and spending time with my family.

William Tollefsen, MD is the EMS and MIH Medical Director for South Shore Health. Dual-boarded in Emergency Medicine and EMS Medicine, Dr. Tollefsen works clinically as an Emergency Physician at South Shore Health in addition to his role as EMS Medical Director.

One of few physicians in the country to receive the prestigious "FAEMS" recognition, Dr. Tollefsen is also the Medical Director for OEMS Region IV, serving 61 cities and towns of the Metro-Boston EMS Council. As the current EMS Medical Director for eight municipal and three private ambulance services on the South Shore, Dr. Tollefsen interacts and provides oversight for over 400 Paramedics.

Dr. Tollefsen graduated from New York Medical College and completed residency training in Emergency Medicine at Harvard University, Brigham and Women's, and Massachusetts General Hospital. He completed a fellowship in Emergency Medical Services and Critical Care Transport at the University of Massachusetts, where he worked as an Emergency Physician and Flight Physician for UMASS LifeFlight. He completed an MBA at the Isenberg School of Management at UMASS Amherst, and holds a Master of Medical Science degree from the Boston University School of Medicine.

A former pre-hospital provider, he is actively involved in EMS system design, paramedic education and Critical Care Transport Systems. He works closely with multiple EMS, Fire and Law Enforcement agencies throughout Massachusetts.

His research interests include systems of care, resuscitation, airway management, and paramedic education.