Background: Patients with an incisional hernia often wait a significant period of time from the first referral to hernia surgery because of waiting lists, watchful waiting, or the need for preoperative optimization. It is unknown if hernia dimensions or patient-reported symptoms increase during this period. The aim of the study was to examine if incisional hernias increase in size during the time from initial assessment to surgical repair. Materials and methods: A prospective controlled trial was performed on patients referred to a regional hernia center for repair of an incisional hernia with a transverse fascial defect of >7 cm. All patients underwent computed tomography scans and answered the Hernia-Related Quality of Life Score questionnaire and International Physical Activity Questionnaire at first assessment and again 30 ± 2 wk later or immediately before hernia repair. Changes in fascial defect sizes and hernia sac volume were assessed along with the patient-reported outcomes. Results: A total of 35 patients were included. The median fascial defect area increased from 117.3 cm² (interquartile range 46.5-181.2) to 150.4 cm² (62.5-199.0), P < 0.001, and the median hernia sac volume increased from 5.11 L (2.28-8.09) to 6.25 L (3.03-10.38), P < 0.001. There were no significant changes in the patient-reported outcomes. Conclusions: Incisional hernias expand during the period from the first assessment to actual hernia repair.