Background: Therapy with oral anticoagulation (OAC) can be challenging, especially in high risk groups such as chronic patients. Gaps in patient knowledge about OAC are linked to reduced effectiveness and safety of treatment. The objectives of this study were i) to assess OAC knowledge gathered during an intermediate medication review (MR) in patients taking vitamin K antagonists (VKA) or non-vitamin K antagonist oral anticoagulants (NOAC); ii) to assess OAC knowledge two weeks after the MR, and iii) to evaluate patient satisfaction with the MR service in community pharmacies. Methods: Chronic OAC patients were invited for a regular MR service in Swiss community pharmacies, the so-called “Polymedication-Check” (PMC). OAC knowledge was assessed with seven newly generated items asked face-to-face during a PMC and by telephone two weeks later. Knowledge gaps, pharmacists’ spontaneous interventions, and patient satisfaction were documented by observing pharmacy students. Treatment groups were compared. Results: Of all patients (n = 81), the number of patients with one or more knowledge gaps decreased from 66% to 31.3% after PMC (p < 0.001). NOAC patients (n = 31) had more knowledge gaps than VKA patients (n = 50; p < 0.05). Most patients (98.6%) were satisfied with the counselling provided by the pharmacists. Conclusion: The majority of chronic OAC patients shows knowledge gaps. Although spontaneous, the provision of tailored education during a PMC increased patient OAC knowledge.