Obesity is becoming more common in the United States, affecting > or = 30% of adults aged 20 years and older. Obesity (body mass index 30) is ranked second only to tobacco use as a preventable cause of death in the United States. Roux-en-Y gastric bypass (RYGBP) is being performed at a rapidly increasing rate, and laparoscopic Roux-en-Y gastric bypass (LRYGBP) surgery is frequently chosen rather than an open approach because of lower morbidity rates. One of the complications of LRYGBP includes small bowel obstruction (SBO) secondary to internal herniation. When RYGBP is performed through the open approach, SBO is most commonly caused by adhesions. The challenge with these patients is that the presenting signs, symptoms, and physical and radiological examinations may be vague, nonspecific, and/or nondiagnostic. Internal hernias that result as a complication of LRYGBP occur in 1 of 3 places. These locations include the transverse mesocolon, the jejunal mesenteric defect at the level of the jejunojejunostomy, and Petersen's space, which is the area between the mesentery of the Roux limb and the transverse mesocolon. We report the case of a 45-year-old woman who presented with SBO secondary to Petersen's hernia. The clinical presentation and radiologic studies are discussed.