OBJECTIVES: Controlling moderate-to-severe pain remains a major challenge after cardiothoracic surgery. Several outcomes have been compared extensively after valve surgery performed via midline sternotomy versus mini-thoracotomy, but postoperative pain (POP) was not adequately examined. Therefore, the authors tested the hypothesis that there is no difference in POP trajectories in patients undergoing valve surgery via midline sternotomy versus mini-thoracotomy. DESIGN: An Institutional Review Board-approved retrospective study. SETTING: At a single, large academic medical center. PARTICIPANTS: Adult patients who underwent mitral or aortic valve surgeries over a 5-year period. INTERVENTIONS: The authors compared the characteristics of pain between valve surgery patients receiving either midline sternotomy or mini-thoracotomy. To identify pain score trajectories, the authors employed latent class linear mixed models and then used multinomial regression models to study the association between incision type and pain trajectory class. MEASUREMENTS AND MAIN RESULTS: The authors' cohort consisted of 1,660 surgical patients-544 (33%) received a midline sternotomy, and 1,116 (66%) received a mini-thoracotomy. The authors identified the following 4 pain trajectory classes: stationary, rapidly improving, slowly improving, and acute worsening pain. Compared to the rapidly improving class, the odds of belonging to the stationary (adjusted odds ratio [aOR] [95% CI] 1.45 [1.01- 2.08]; p = 0.04) or the acute worsening class (aOR [95% CI] 1.71 [1.10-2.67] p = 0.02) were significantly higher for sternotomy patients compared to mini-thoracotomy. CONCLUSIONS: Midline sternotomies are associated with higher odds of having an acute worsening or stationary versus a rapidly improving pain trajectory compared to mini-thoracotomies. Therefore, the choice of incision may play an important role in determining POP trajectory after valve surgery.