Urinary bladder augmentation with segments of the stomach (gastrocystoplasty), small bowel, or large intestine (enterocystoplasty) improves capacity and compliance in patients with bladder dysfunction. Although malignant complications of enterocystoplasty have been reported, the risk of malignancy in the setting of gastrocystoplasty is not known. We describe the case of a 73-year-old woman who developed a transitional cell carcinoma associated with transitional cell metaplasia and dysplasia of the gastric epithelium 14 years following gastrocystoplasty. To our knowledge, this is the first reported case of a malignant complication of this surgical procedure. We conclude that patients who have undergone gastrocystoplasty are at an increased risk for the development of malignancy in the neobladder and require close long-term follow-up, similar to patients who have undergone enterocystoplasty.