Hypertension remains the most important cardiovascular risk factor in Poland. May Measurement Month is a global initiative organized by the International Society of Hypertension aimed at raising awareness of hypertension and the need for blood pressure (BP) screening and demonstrating the potential of the opportunistic BP measurements. An opportunistic cross-sectional survey of volunteers aged ≥18 was carried out in 146 sites in May 2018. Blood pressure was measured in 6450 subjects (mean age: 41 ± 15 years; 59% females). After multiple imputation, the age and sex standardized systolic and diastolic BP was 126.7/78.4 mmHg in the whole analysed group, 132.8/81.3 mmHg in subjects taking antihypertensive drugs, and 125.7/78.0 mmHg in those not taking any antihypertensive drugs. After multiple imputation, the proportions of subjects with high BP (systolic ≥140 mmHg or diastolic ≥90 mmHg or on treatment for raised BP) were 22.2% in the whole analysed group, 39.2% in subjects taking antihypertensive drugs, and 18.6% those not taking any antihypertensive drugs. Overall, hypertension was present in 32.8% of participants, among them 38.7% were not aware of the disease, 53.1% were taking antihypertensive drugs, and 32.3% had BP controlled to target (<140/90 mmHg). Blood pressure was increasing with increasing body mass index and alcohol intake. Smokers and project participants with diabetes had increased average BP. In conclusion, this project provides additional evidence for a considerable potential for further reduction of cardiovascular risk through improvement in detection and treatment of hypertension in Poland.