The combination of hypophosphataemia and hypercalcaemia has numerous aetiologies, which can be challenging in the clinical setting. Careful early biochemical identification will facilitate appropriate further imaging and management. We report a case of a gentleman who presented in his ninth decade with deteriorating cognition, proximal muscle weakness and reduced mobility on a background of hypertension, type 2 diabetes with associated retinopathy and stage 3 Chronic Kidney Disease (CKD). On admission biochemistry revealed hypophosphataemia (0.70 mmol/L), hypercalcaemia (3.42 mmol/L), an elevated serum alkaline phosphatase but a suppressed serum parathyroid hormone (PTH) with a low vitamin D level (47.7). The overall picture was consistent with non PTH mediated hypercalcemia secondary to oncogenic osteomalacia. No elevation in tumour markers including prostate specific antigen, alpha feto protein and serum beta-hCG was observed. In order to delineate underlying aetiology it was agreed for him to undergo CT of chest, abdomen and pelvis which revealed evidence of disseminated intra thoracic and abdominal malignancy and a primary gastric malignancy which was evident as linitis plastica. His initial hypercalcemia was managed conservatively and hypophosphatemia reversed with intravenous incrementation. It led to objective improvement in his cognition and mobility. Oncogenic ostemalacia is a challenging diagnosis and overall aetiology is mediated by fibroblast growth factor 23 (FGF23) leading to tubular phosphate wasting and impaired Vitamin D hydroxylation associated with low 1α-hydroxylase activity. This case highlights importance of timely recognition of this difficult pathology. We advocate the use of early imaging in to facilitate early recognition of underlying tumour load and timely treatment. There might be a role for FGF 23 measurement in clinic setting to aid advance decision making.