A 31-year-old primigravid female presented to the obstetric department with severe left flank pain at 27 weeks' gestation. Her pregnancy had otherwise been straightforward and there was no significant past medical history. Physical examination was unremarkable apart from some vague tenderness and fullness in the left upper quadrant, and routine blood tests and urinalysis revealed no abnormalities. Obstetric ultrasound confirmed a 27-week gravid uterus with a single live fetus. Analgesia was administered and an ultrasound scan of her abdomen requested for the next morning. Over the next few hours her abdominal pain got progressively more severe and the patient became increasingly distressed. Further examination revealed her to be hypotensive (blood pressure 85/40 mmHg), tachycardic and tachypnoeic with obvious central cyanosis (SpO2 88% on room air). Auscultation of her chest revealed decreased air entry over the left lung and tracheal shift to the right. An urgent chest X-ray suggested left diaphragmatic herniation of abdominal contents (Figure 1). Insertion of a nasogastric tube was attempted without success. Owing to increasing hypoxia and respiratory distress a decision was made to intubate and ventilate the patient before transfer to theatre. Emergency laparotomy revealed at least 3.5 litres of blood within the peritoneal cavity and a large congenital defect in the postero-lateral portion of the left hemi-diaphragm (Bochdalek hernia). Most of the small bowel, the whole of the transverse colon and the stomach with the attached spleen had herniated through the defect causing the left lung to collapse. The abdominal contents were reduced back into the abdominal cavity, and the diaphragmatic defect repaired. A dead fetus was removed by caesarean section. The patient required several weeks of intensive therapy, and her recovery was complicated by pancreatitis which required laparotomy for desloughing of necrotic pancreatic tissue. She eventually went on to make a full recovery, and has subsequently had a healthy baby.