Recent data regarding the prevalence and determinants of undiagnosed hypertension in Saudi Arabia are particularly lacking. This study aimed to investigate the prevalence of undiagnosed hypertension and to identify potential associates of hypertension risk among adults in the Western region of Saudi Arabia. Cross-sectional data for 489 Saudi adults were collected from public places in the cities of Madinah and Jeddah. Demographic, anthropometric (height, weight, waist circumference), and blood pressure (assessed by a digital sphygmomanometer) data were collected from all participants during face-to-face interviews. The American College of Cardiology and American Heart Association guidelines were used to evaluate blood pressure status. Sodium intake was assessed using a semi-validated food frequency questionnaire. The prevalence of undiagnosed, elevated blood pressure, stage I, or stage II hypertension was 9.82%, 39.5%, and 17.2%, respectively. The proportions of individuals with undiagnosed hypertension were higher among men and smokers (p < .001 for both). Blood pressure status was positively associated with weight, body mass index, and waist circumference among participants (p < .001 for all). Higher body mass index and waist circumference were associated with increased odds of stage I and stage II hypertension. Sodium intake was not associated with blood pressure status. A strikingly high prevalence of undiagnosed hypertension was observed among the study sample. National intervention programs are necessary to encourage regular screening and follow-up for the early detection and management of hypertension.