Background Stoma site incisional hernias after ileostomy closure are complex hernias that can be associated with abdominal pain, discomfort, and a diminished quality of life. The aim of this study was to determine the incidence of incisional hernia (IH) following temporary ileostomy reversal in patients undergoing colorectal surgery, and the risk factors associated with its development. Methods This was a prospective, single-centre, cohort study of patients undergoing ileostomy reversal between January 2010 and December 2016. Comorbidities, operative characteristics, comparison between early and late ileostomy closure and postoperative complications were analysed. Results A total of 202 consecutive patients were prospectively evaluated (median follow-up 46 months; range: 12–109). Stoma site incisional hernia occurred in 23% of patients (n = 47), diagnosed by physical examination or imaging tests. The reasons for the primary surgery were colorectal cancer (n = 141, 69.8%), inflammatory bowel disease (n = 14, 6.9%), emergency surgery (n = 35, 17.3%), and other conditions (n = 12, 5.9%). Secondary outcomes: a statistically significant risk factors for developing an IH was obesity (higher BMI) (OR 1.15, 95% CI: 1.05–1.26) p = .003). Conclusions 23% of patients developed surgical site IH, a higher BMI being the only risk factor found to be statistically significant in the development of an incisional hernia.