Although canalicular injury (CI) is a known complication of periocular Mohs micrographic surgery (Mohs), there is a dearth of literature describing the causes of CI after Mohs. The purpose of this research was to identify potential risk factors for CI following Mohs surgery. The data may be used in pre- and post-operative patient counseling and surgical preparation. This case-control study compared patients who needed ophthalmologic Mohs repair after canalicular injury to those who did not. The control group consisted of all subjects who were included in the Mohs CI study. Other causes of CI were ruled out. The most prevalent primary tumor was basal cell carcinoma (P<.00001). Infiltrative, morpheaform, and/or micronodular basal cell carcinomas were more common in people with canalicular damage. There was no significant difference between cases and controls regarding the initial tumor location involving the medial canthus (32% vs 17%, P=.22). Final defects in the medial canthus were more common in cases than in controls (55% vs. 26% P=.01952). In spite of the fact that the medial canthus was involved in the majority of cases, many tumors that resulted in CI did not appear to have spread to that area at first. Predicting the need for canalicular reconstruction is difficult, and surgeons cannot rely solely on anatomical location when making CI risk assessments.