The skeletal system is a frequent site for metastases of urothelial carcinoma (UC) of the bladder (22-37%). Of those cases involving bone, the marrow is infiltrated in 27% of patients. Imaging modalities, such as X-ray and CT, will detect gross skeletal lesions in the vast majority of these patients with bone marrow involvement, however, most patients with bone involvement are symptomatic at presentation. Additionally, there have been few reports in the literature of bone marrow metastases from UC presenting with isolated thrombocytopenia. This case report describes the case of a 53-year-old male with muscle-invasive transitional cell carcinoma of the bladder treated with cystoprostatectomy. Preoperative evaluation was significant only for mild thrombocytopenia. Standard workup for metastatic bony involvement, which included history, physical, chest X-ray, and whole body CT, was negative. Postoperatively, the patient's thrombocytopenia worsened and he bled diffusely from his pelvic bed. Bone marrow biopsy was obtained and showed the entire marrow cavity to be filled with metastatic transitional cells. In the event of a similar future presentation of isolated thrombocytopenia in the setting of invasive UC, the clinician should consider a bone marrow biopsy, in addition to the standard workup for metastatic bony involvement, prior to proceeding with any surgical intervention.