Pulmonary hypertension (PH) is a common sequela of degenerative mitral valve disease, but the regression of PH after mitral surgery is often incomplete. We sought to identify the preoperative risk factors for residual PH after mitral valve repair and its effect on the clinical outcome. The outcomes in 71 patients with preoperative PH (mean pulmonary arterial pressure ≥25 mm Hg) were compared according to the presence or absence of residual PH 24 hours after mitral valve surgery. Of 71 patients, 33 (46%) had residual PH. The remainder experienced significant reductions in the mean pulmonary arterial pressure without changes in pulmonary vascular resistance. Patients with residual PH had significantly elevated postoperative pulmonary vascular resistance (despite a significant decrease from the preoperative baseline) compared to those without residual PH. Residual PH was an independent risk factor for postoperative morbidity, mortality, and a prolonged intensive care unit stay (odds ratio 4.0, 95% confidence interval 1.2 to 13.1, p = 0.02), independent of the preoperative mean pulmonary arterial pressure. A decreased left ventricular ejection fraction (odds ratio 0.9, 95% confidence interval 0.8 to 1.0, p = 0.007) and fibroelastic deficiency (odds ratio 3.6, 95% confidence interval 1.1 to 11.8, p = 0.03) were independent predictors of residual PH. In conclusion, residual PH is a clinically important entity common after mitral valve repair for degenerative disease and is associated with clinical variables that aid in the preoperative prediction of at-risk patients.