We present a case of a severe anaphylactic reaction to diclofenac, administered as an intravenous infusion in a 45-year-old patient, during intravenous anesthesia for in vitro fertilization. During the preoperative clinical examination and obtaining of anamnestic data, the patient denied symptoms of allergies to medicines and other substances. The dominant clinical manifestations of anaphylactic reaction were: hypotension, tachycardia, angioedema, bronchospasm, and delayed awakening following anesthesia. No visible changes in the appearance of the skin, such as erythema or urticaria have been observed. Proper clinical observation and adequate intraoperative monitoring led to rapid diagnosis and significantly reduced the time interval from the onset of anaphylaxis to the beginning of treatment and reanimation procedures.