Summary We report a case of spontaneous tumour lysis syndrome that developed postoperatively in a patient with undiagnosed Burkitt’s lymphoma. The former diagnosis was made, unusually, following the development of white emulsion‐like urine in the catheter bag whilst the patient was being managed in the intensive care unit. After laboratory analysis, the urine was found to contain large quantities of uric acid crystals which were the key to the prompt diagnosis. Spontaneous tumour lysis syndrome is rare and this case highlights the difficulties in making an early diagnosis when the presence of a predisposing tumour has not yet been identified. Untreated tumour lysis syndrome can be fatal due to severe biochemical disturbances causing cardiac dysfunction and multi‐organ failure. Early recognition and treatment are crucial to prevent morbidity and mortality. The unusual presentation of this case in association with an undiagnosed Burkitt’s lymphoma emphasises how vigilant anaesthetists and intensivists must be in recognising this potentially life‐threatening condition. We believe that the triggering factor in this case was laparotomy and handling of the tumour.