There are currently few recommendations on how to assess inter-arm blood pressure (BP) differences. The authors compared simultaneous with sequential measurement on mean BP, inter-arm BP differences, and within-visit reproducibility in 240 patients stratified according to age (<50 or ≥60 years) and BP (<140/90 mm Hg or ≥140/90 mm Hg). Three simultaneous and three sequential BP measurements were taken in each patient. Starting measurement type and starting arm for sequential measurements were randomized. Mean BP and inter-arm BP differences of the first pair and reproducibility of inter-arm BP differences of the first and second pair were compared between both methods. Mean systolic BP was 1.3±7.5 mm Hg lower during sequential compared with simultaneous measurement (P<.01). However, the first sequential measurement was on average higher than the second, suggesting an order effect. Absolute systolic inter-arm BP differences were smaller on simultaneous (6.2±6.7/3.3±3.5 mm Hg) compared with sequential BP measurement (7.8±7.3/4.6±5.6 mm Hg, P<.01 for both). Within-visit reproducibility was identical (both r=0.60). Simultaneous measurement of BP at both arms reduces order effects and results in smaller inter-arm BP differences, thereby potentially reducing unnecessary referral and diagnostic procedures.