Iron-induced hypophosphatemia represents an increasingly recognised complication of iron infusion. A 34-year-old woman presented for surgical management of her colorectal cancer. Post-operative blood tests revealed severe hypophosphatemia, resistant to oral phosphate supplementation and large volumes of intravenous phosphate replacement. Further questioning and biochemical investigation led to the recognition of iron-induced hypophosphatemia as a contributory cause, secondary to iron infusion administered as part of pre-operative optimisation. Early consideration, diagnosis and management of this complication has the potential to reduce fluid burden associated with intravenous phosphate supplementation and optimise post-operative care.