BACKGROUND: In the laparoscopic Roux-en-Y gastric bypass procedure, the gastrojejunal stoma is constructed with either a circular (CSD) or a linear stapling device (LSD). The diameter of the stoma following stapling with the 21 mm CSD is expected to be approximately 12 mm (diameter of the anvil). Measuring the stoma diameter after linear stapling is a little more complex since the remaining opening in the linear anastomosis is closed by hand. The aim of this prospective randomized study was to follow up on changes in the diameter of gastrojejunal stomata after laparoscopic Roux-en-Y gastric bypass using either a CSD or an LSD between that at construction and at a long-term follow-up of 12-72 months later. METHODS: Twenty patients were randomly assigned to gastrojejunostomy with either a 21 mm CSD or a 45 mm LSD. Directly after completion of the surgery, the diameter of the gastrojejunal stoma was measured using a Fogarty occlusion catheter and again at follow-up 12-72 months later. RESULTS: Five patients were lost for follow-up, and 15 patients remained. The mean diameter of the CSD stomata at construction was 19.3 ± 5.3 mm (mean ± SD) and increased to 26.4 ± 6.6 mm at follow-up after a mean of 46 months (P = 0.02). The corresponding figures for the LSD stomata were 26.2 ± 4.1 mm, increasing to 32.7 ± 3.0 mm also after a mean follow-up of 46 months (P = 0.03). CONCLUSIONS: The mean diameter of the circular stapled gastrojejunostomy stomata at construction was 20 mm, that is, considerably larger than the 12 mm expected. After a mean of 5 years, the mean diameter had increased by 37%. The mean diameter of the linear stapled stomata increased by 25%.