Combined duplication of the colon and vermiform appendix is one of the rare congenital anomalities of the alimentary tract. Only a few cases have been reported in the adult population. A 28-year-old man presented to the clinic with a mass in the right flank. Imaging showed only a hydronephrotic atrophic kidney. The final diagnosis was only available at exploration. Combined duplication of the tubular colon and vermiform appendix was confirmed histopathologically. The patient was treated with nephrectomy and complete resection of the duplicated colon and vermiform appendix. The patient recovered uneventfully, and has done well for the past year. This is believed to be one of the first reports of combined duplication of the tubular colon and vermiform appendix as a cause of hydronephrotic atrophic kidney in an adult patient.