Adenocarcinomas of the urinary bladder are exceedingly rare and present in various morphological forms. Virtually all of these are identical to glandular malignant neoplasia native to topographically neighboring organs, where the incidence of adenocarcinoma is also much more common, such as the large intestine. Cases of glandular malignancies of the urinary bladder, therefore, require not only a detailed histopathological evaluation and interpretation but also a detailed clinical and radiological one. These should be performed with the goal of proving the origin of the tumor as one arising from the urinary bladder and not an entry originating from another organ and invading or producing metastasis to it. A controversial etiopathogenic link to urinary bladder adenocarcinoma is that of cystitis cystica et glandularis, which often coexists with the condition. Herein, we present a case report of non-muscle-invasive urinary bladder adenocarcinoma in a previously healthy male patient in his forties with a known history of cystitis cystica et glandularis. The patient presented with gross hematuria, and based on his known urological condition, a cystoscopy with biopsy was performed, showing submucosal proliferation of atypical glands. The detailed clinical and radiological evaluation showed no evidence of malignancy at other sites. As the malignancy was non-muscle-invasive, an intravesical dose of the Bacillus Calmette-Guérin vaccine was administered. The patient was followed up with cystoscopy, and a biopsy showed no evidence of residual malignancy, with cystitis cystica et glandularis persisting. A year following the diagnosis, the patient is still actively monitored, and no recurrence is noted.