Adrenal vein sampling (AVS) is essential in differentiating unilateral from bilateral sources of aldosterone excess in primary aldosteronism (PA). However, its ability to predict blood pressure (BP) improvement after adrenalectomy has not been well studied. This is a retrospective observational study of 119 patients who underwent AVS by sequential technique followed by adrenalectomy for PA at the Hospital of the University of Pennsylvania from 1997 to 2015. Median age was 52 years (interquartile range 44-59), 67% were male and median duration of hypertension was 10 (interquartile range 6-20) years. A total of 76% and 90% of patients experienced BP improvement at 0-6 months or at any time point after surgery, respectively. Lateralization index (LI) > 8, but not the presence of contralateral suppression, was significantly associated with BP improvement after surgery by multivariate logistic regression analysis adjusted for potential confounders (odds ratio (95% confidence interval): 17.1 (1.7-171.6) and 6.39 (0.06-641.8), respectively). A prediction score was created by covariates that was significantly associated with BP improvement in logistic regression analysis (duration of hypertension, body mass index, preoperative systolic BP and number of antihypertensive medications). Receiver-operating characteristic curve analyses showed that the addition of LI > 8 to the score increased its ability to predict BP improvement (area under the curve 0.73-0.80). In conclusion, LI is useful in predicting improvement in BP after adrenalectomy for PA. The results of this study suggest that patients with long-standing severe hypertension may still benefit from surgery if LI > 8.