Hypercalcemia secondary to hypervitaminosis D is extremely rare. Vitamin D intoxication usually occurs as a result of inappropriate use of vitamin D preparations and can lead to life-threatening hypercalcemia. Here we present a case of a 45-year-old female diagnosed with colon adenocarcinoma stage IV with liver, lung and bone (ribs) metastases, s/p FOLFOX x 6 cycles, s/p FOLFIRI x 2 cycles. She was admitted for 3rd cycle chemotherapy but this was complicated by the development of pneumonia with worsening of kidney function and hemodialysis was initiated. Despite being on regular hemodialysis, her calcium levels were noted to be increasing. She was also noted to be feeling weaker, with a decrease in sensorium attributed to encephalopathy. Workup for hypercalcemia revealed low normal PTH (21.50 pg/mL, N: 14.0-72), with a normal phosphorus level and elevated Vitamin D (104.28 ng/mL, N: 30-50).  It was later revealed upon review of the patient’s medications that her mother was giving her various herbal supplements, the latest of which was one that contained an extract from Agaricus blazei Murrill, a mushroom native to Brazil that allegedly aids in the treatment of a variety of diseases such as cancer, chronic hepatitis, diabetes, atherosclerosis and hypercholesterolemia. Mushrooms are one of the main dietary sources of vitamin D. The probable offending agent was discontinued and the patient was given IV hydrocortisone. Other therapies such as calcitonin and denosumab were not given due to the patient’s history of anaphylactic reactions. Serial monitoring showed that the calcium levels steadily decreased, as well as the Vitamin D levels, although at a slower rate. This case highlights the importance of assessing the intake of all substances, not only prescribed medications, and the potential danger of the ingestion of unlicensed herbal supplements.