Mark A. Casillas, Jr., MD specializes in laparoscopic and robotic colon and rectal surgery for neoplastic and benign disease, transanal endoscopic microsurgery, inflammatory bowel disease including Crohn’s disease and ulcerative colitis, constipation, and functional anorectal disorders.

Dr. Casillas is an Assistant Professor in the Division of Colorectal Surgery in the University of Tennessee Graduate School of Medicine Department of Surgery. He received a Bachelor’s in Microbiology  from the University of Alabama. He completed a Master’s degree in Molecular Biology at the University of Alabama at Birmingham, and earned his Medical Doctorate from the University of Alabama School of Medicine (UAB). He performed his intern year at Brown University School of Medicine and then completed his general surgery training at St. Joseph Mercy Hospital, Ann Arbor. Dr. Casillas completed a subspecialty fellowship in Colon & Rectal Surgery at Indiana University School of Medicine, and joined the faculty of the University of Tennessee Medical Center in 2012.

Dr.  Casillas has written and presented articles and abstracts on a variety of subjects including basic science cancer research, robotic colon and rectal surgery, as well as single incision laparoscopic colon and rectal surgery.

Dr. Casillas is board certified by the American Board of Surgery and board certified by the American Board of Colon and Rectal Surgery.

Dr. Casillas specializes in the diagnosis and treatment of diseases of the colon, rectum, and anus with emphasis on screening and surgical management of colorectal cancer, hemorrhoids, diverticular disease, and inflammatory bowel disease (Crohn's disease and ulcerative colitis). We offer state-of-the-art screening for colon and rectal cancers and treat complex anorectal disorders, including fecal incontinence & sacral nerve stimulation, pelvic floor abnormalities, anal fissures, and fistulas.