Background Laparoscopic Roux-en-Y gastric bypass (LRYGB) is the most commonly used surgical procedure in the treatment of morbid obesity in Denmark. Internal herniation (IH) and intermittent internal herniation (IIH) are probably the most common late complications in patients with LRYGB. The aim of this study was to investigate a possible increased risk of subsequent operations after an initial IH or IIH event. Methods This long-term follow-up study of patients who had surgery for an initial IH or IIH event in 2006–2011, based on the Danish National Patient Registry (NPR), was performed to 2013. During this period, mesenteric defects were not closed routinely during LRYGB. Results Data were retrieved from 12 221 patients with LRYGB from the NPR. A total of 383 patients had surgery for an initial IH or IIH event. Some 102 patients (26·6 (95 per cent c.i. 22·5 to 31·3) per cent) had a second operation. Twenty-seven (26·5 (18·9 to 35·8) per cent) of these 102 patients had a third operation, and five (19 (8 to 37) per cent) of the 27 had a fourth operation. Of the 383 patients diagnosed with an initial IH or IIH event, 72 (18·8 per cent) had a second IH/IIH event, 14 (3·7 per cent) had a third event, and three (0·8 per cent) a fourth event requiring surgery. Conclusion Patients who have surgery for IH or IIH have a substantial risk of needing further operations.