Leptomeningeal carcinomatosis (LC) is a rare leptomeningeal spread of diffusely metastatic tumors. It occurs more commonly with hematologic tumors, less commonly with solid tumors, and is exceedingly rare in prostate cancer. Due to its scarcity, it has traditionally been difficult to diagnose LC but advancement of MRI has helped considerably. However, even with technological improvements, pre-mortem diagnosis of LC remains difficult and controversial. Our case is a 71-year-old male with prostate cancer with bone metastases who presented to our facility with altered mental status (AMS), lower extremity weakness, and worsening diarrhea. The diarrhea was responsive to antibiotic therapy, but his AMS did not resolve. A head CT without contrast was negative but follow-up brain MRI revealed leptomeningeal enhancement highly suggestive of LC. Cerebrospinal fluid (CSF) cytology results were negative and other CSF studies were inconclusive. Although further studies were planned, the patient continued to deteriorate, and the family elected to withdraw care. He passed away without beginning treatment for the LC. Despite advances in cancer therapies, LC remains difficult to diagnose and treat. Imaging may be suggestive of the condition but the confirmatory tests such as repeated CSF cytology or meningeal biopsy are not only invasive but also usually occur postmortem. Additional methods of CSF testing have been studied to evaluate their role in accurately diagnosing LC but low specificity for LC has somewhat limited their use. Although treatment options are mainly palliative in nature, prompt recognition and early treatment could grant valuable time for patients and families.