Elevated blood pressure (BP) is the single most important contributing risk factor to the global disease burden, leading to over 10 million deaths each year. In Spain, hypertension (HTN) affects around 20% of the adult population and remains the greatest attributable cause of cardiovascular mortality. May Measurement Month (MMM) is a worldwide initiative aimed at increasing awareness of HTN and to improve the lack of screening programmes worldwide. An opportunistic cross-sectional survey of volunteers aged 18 and over was carried out in May 2018. Blood pressure measurement, the definition of HTN and statistical analysis followed the standard MMM protocol. Anthropometric data and responses to questionnaires on demographic, lifestyle, and environmental factors were obtained as additional information. Screening sites mainly in community pharmacies, universities, primary care centres, HTN units, and cardiovascular departments in hospitals were set up across Spain as part of this initiative. In total, 7646 individuals (63.5% female) were screened during MMM18. After multiple imputation, 40.0% had HTN, of whom 74.4% were aware of their diagnosis and 69.6% were taking antihypertensive medication. Of individuals not receiving antihypertensive medication, 16.9% were hypertensive. Of individuals receiving antihypertensive medication, 36.4% had uncontrolled BP. MMM18 almost doubled the number of participants of MMM17 and was the largest BP screening campaign ever undertaken in Spain, showing that in the absence of systematic screening programmes for HTN, MMM can identify a great number of individuals at risk, increasing their awareness and attracting the interest of the healthcare system in Spain.