The analysis in hand conducts an assessment of the need of implementingthe International Ship and Port Facility Security Code (ISPS Code) instruments- as established by the International Maritime Organization (IMO) - and particularlythe Port Facility Security Assessment (PFSA) and Port Facility SecurityPlan (PFSP) at Customs Maritime Units. This research effort examines the securityat Mexican Customs Maritime Units’ installations at different ports fromthe ISPS Code perspective. To study these phenomena, Harbour Masters, theCommanders of the Navy, Directors of Customs Units, Port Facility SecurityOfficers and Port Directors from eighth of the most important Mexican portswere interviewed on the subject to identify the challenges and opportunities forimproving maritime and port security. Additionally, the customs maritime units’installations were visited for direct observation. The results demonstrate the negativeeffect of customs agents’ rotation between airport customs units, bordercustoms units and Customs Maritime Units, as well as the need for the developmentand implementation of PFSAs and PFSPs not only at ports and port terminals,as required by the ISPS Code, but also at the Customs Maritime Unitsinstallations, which are within the port installations. The findings show that inMexico, more than 40% of port and maritime security incidents occurred at theCustoms installations during the year of 2017. The lack of security assessmentsand security plans that relate to Customs Maritime Units put in risk to the wholeport facility and its terminals. Therefore it is recommended the establishment ofa national department within the Customs Authority to lead the development ofsecurity assessments and security plans but in accordance with the specificationsof the ISPS Code, aiming for a harmonization between “Customs SecurityPlans” and PFSP. This will ensure that security procedures established at CustomsMaritime Units are synchronized with those from the port facility in caseof serious security incidents. Finally, the urgent need for providing maritime and port security training related to ISPS Code requirements and procedures to customs’police personnel serving in Customs Maritime Units was identified. Theoreticaland practical implications are discussed for researchers and practitionersin the areas of maritime security and future research directions are provided.