The aim of this prospective observational study was to determine the effects of progressive preoperative pneumoperitoneum (PPP) on the size of large incisional hernia (IH) and abdominal muscles by abdominal computed tomography (CT) scan. PPP was performed in 18 patients. All IH were large. A mean volume of 12.8 l was insufflated over a mean period of 14.8 days. Respectively, before and after PPP, the mean IH height and width was 117 and 130 mm (P < 0.05) and 101 and 115 mm (P < 0.05), the mean width of the right and left rectus abdominis was 99 and 109 mm (P < 0.05) and 100 and 113 mm (P < 0.05), and the length of the right and left anterolateral muscles was 198 and 233 mm (P < 0.05) and 185 and 210 mm (P < 0.01). In conclusion, PPP increases the abdominal wall muscle length and has the same impact on the IH orifice. PPP would facilitate the fascial repair of otherwise untreatable large IH.