Saint Mary's Hospital (abbreviated STMH) is a Yale-affiliated urban hospital located at 56 Franklin Street, Waterbury, Connecticut. Operated by Trinity Health, it was founded in 1907 by the Sisters of Saint Joseph of Chambéry and is designated as a Level II trauma center. Saint Mary's has been a teaching hospital for the Yale University School of Medicine for over 40 years.

In 2011, Waterbury Hospital and St. Mary's Hospital said they planned on merging. The merger between St. Mary's Hospital and Waterbury Hospital was called off in 2012.

In July 2014 Tenet Healthcare announced that the hospital would be acquired by a Tenet subsidiary, with the hospital's religious directives and uncompensated care policies remaining intact. Tenet was chosen by the hospital after a four-year selection process. The Tenet deal unraveled in 2015 when Tenet expressed concern with the conditions on the sale set by the state of Connecticut.

In September 2015, Saint Mary's Hospital was acquired by Livonia, Michigan-based Trinity Health, who had recently acquired Saint Francis Hospital & Medical Center in Hartford. In 2018, Trinity Health opened a center for multiple sclerosis treatment and research at the hospital.

The HealthGrades website contains quality data for St. Mary's Hospital as of 2016. For this rating section three different types of data from HealthGrades, 9 or 10 are the two highest possible ratings. Percentage of patients rating this hospital as a 9 or 10 - 67%.

• St. Mary's Hospital (Waterbury) website

41°33′11″N 73°02′12″W / 41.5531°N 73.0368°W / 41.5531; -73.0368