revealed suboptimal adherence. Investigators developed a multitiered intervention program that included pamphlets, lecturers, and posters of the Checklist for the OR; the impact of these interventions on adherence has not been described. We hypothesized: 1) Interventions will improve Checklist adherence; and 2) Adherence is associated with positive perceptions about the Checklist and use of the Educational Interventions.Methods: Between 06/2014 and 08/2014, a serial cross sectional study design was implemented at two hospitals. Surgical observations measured verbal confirmation of the WHO Checklist's 19 steps by the appropriate surgical staff in their prescribed order ("pre-anesthesia", "pre-incision", "pre-exit from the OR"). Questionnaires were administered to surgeons, anesthesiologists, and nurses. Questionnaires assessed perceptions of the Checklist, interventions, and surgical safety. Responses were compared among surgical staff position and hospital site using ANOVA, T-test, and Chi-squared analyses.Findings: 45 surgeries were observed. Adherence to "pre-incision" Checklist items decreased significantly from 2014 to 2015 (P ¼ 0.026). The questionnaire response rate was 93%, with a total of 91 questionnaires administered. On a 1-10 scale, the mean rating of Checklist effectiveness was high, at 9.01 (SD ¼ 1.54). There was no association between adherence and Checklist perceptions or educational intervention use. Perceived unavailability of hard copies of the Checklist, lack of time and motivation to complete the Checklist were frequently identified barriers to adherence.