Objective: The World Health Organization's STEPwise approach to surveillance (STEPS) recommends three standard blood pressure measurements over five minutes (SBPM) to monitor trends of hypertension in low-income countries. The objective of this study was to assess the diagnostic accuracy of SBPM, same-day and next-day unattended automated measurement (uABP), with 24hr ambulatory measurement (24h-ABPM) as reference during a population-based prevalence survey in Lesotho. Design and method: Participants with elevated SBPM (> = 140/90 mmHg) and age- and sex-matched participants with normal SBPM during a household-based survey were recruited. For SBPM and uABP, participants sat and rested for 5 minutes before three measurements were taken each 2 min apart. For both, the mean of second and third measurements was taken as final blood pressure. 1st uABP readings were obtained on survey day. Afterwards participants received a 24h-ABPM device. 2nd uABP readings were taken 24h later after retrieval of the 24h-ABPM. Discrimination was determined for all screening measurements (SBPM, 1st, 2nd uABP) using area under the receiver operating characteristic curve (AUROC), and 24h-ABPM as reference. Results: We enrolled 275 participants [mean age 58 years, 163 (59%) female], 183 with elevated and 92 with normal SBPM. Mean difference between systolic daytime 24h-ABPM and screening measurements was highest for SBPM (mean difference: -12 mmHg; 95%CI: -14 to -9). Mean difference between diastolic daytime ABPM and diastolic SBPM was -2 mmHg (95%CI: -3 to -0.7), whereas no difference was found for mean diastolic 1st uABP (mean difference: -0.6 mmHg; 95%CI: -1.9 to 0.6); and mean diastolic 2nd uABP (mean difference: 1.0 mmHg; 95%CI: -0.4 to 2.4). Misclassification as having hypertension (Figure 1) was highest with SBPM (55 [20%]), followed by 1st uABP (27 [9.8%]) and 2nd uABP (18 [6.5%]). Using systolic daytime 24h-ABPM as reference, the uABPs had higher AUROC (1st uABP: 87% [95%CI: 83-91]; 2nd uABP: 88% [95%CI: 84-92]); SBPM: (79% [95%CI: 74-85]). This difference was significant between 1st uABP and SBPM (p = 0.002), and between 2nd uABP and SBPM (p<0.001). Conclusions: uABP measurements had better diagnostic performance compared to SBPM. Integration of uABP into the STEPS protocol should be considered.