We describe a case of intraoperative gelatine-induced anaphylaxis whose diagnosis was delayed as the use of gelatine during surgical procedures was omitted for two times in patient's medical records. The subject is a 66-year old woman, with a negative medical history of atopy, food and drug allergy, with arterial hypertension on a course of beta-blockers and with bladder carcinoma requiring surgery. The patient had tolerated both general and local anaesthesia on several previous occasions. On the first occasion she experienced arterial fibrillation secondary to a severe episode of hypotension following local anaesthesia, while on a course of beta-blockers. On the second occasion she developed a very severe episode of hypotension followed by the outbreak of a generalised rash during general anaesthesia. The tryptase sera level was 109 mg/L one hour after the reaction had subsided, while the basal values were normal. On the third occasion the patient redeveloped severe hypotension and a generalised rash during general anaesthesia. The allergological work-up was negative, except for intradermal test with gelatine. A study of the intra-cellular cytokines in blood lymphocytes showed a production of IL4 from CD4+ lymphocytes after stimulation by gelatine. The patient underwent a successive surgical procedure without any adverse event.