BACKGROUND: Internal Medicine (IM) programs offer elective subspecialty rotations in which residents may enroll to supplement the experience and knowledge obtained during general inpatient and outpatient rotations. Objective evidence that these rotations provide enhanced subspecialty specific knowledge is lacking. The purpose of this study was to determine whether exposure to an endocrinology subspecialty rotation enhanced a resident's endocrinology-specific knowledge beyond that otherwise acquired during IM residency. METHODS: Data were collected on internal medicine resident scores on the American College of Physicians Internal Medicine In-Training Examinations (IM-ITE) for calendar years 2012 through 2018 along with enrollment data as to whether residents had completed an endocrinology subspecialty rotation prior to sitting for a given IM-ITE. Three hundred and six internal medicine residents in the University of Minnesota Internal Medicine residency program with 664 scores total on the IM-ITE for calendar years 2012 through 2018. Percentage of correct answers on the overall and endocrine subspecialty content areas on the IM-ITE for each exam were determined and the association between prior exposure to an endocrinology subspecialty rotation and percentage of correct answers in the endocrinology content area was analyzed using generalized linear mixed-effects models. RESULTS: Two hundred and thirty-three residents (76%) completed an endocrinology subspecialty rotation at some point during their residency; 121 (40%) residents had at least one IM-ITE both before and after exposure to an endocrine subspecialty rotation. Exposure to an endocrinology subspecialty rotation exhibited a positive association with the expected IM-ITE percent correct on the endocrinology content area (5.5% predicted absolute increase). Advancing year of residency was associated with a predicted increase in overall IM-ITE score but did not improve the predictive model for endocrine subspecialty score. CONCLUSIONS: Completion of an endocrinology subspecialty elective was associated with an increase in resident endocrine specific knowledge as assessed by the IM-ITE. These findings support the value of subspecialty rotations in enhancing a resident's subspecialty specific medical knowledge.