Paravertebral anaesthesia is a particularly effective, safe and reliable option in scoliosis patients undergoing anterior release in whom percutaneous epidural placement may be difficult to perform. A recent systematic review and meta-analysis of randomized trials has demonstrated that whilst paravertebral block and thoracic epidural insertion provide comparable pain relief after thoracic surgery, paravertebral block placement is associated with a better side effect profile, including a reduction in pulmonary complications, hypotension, nausea and vomiting and urinary retention. We describe a case of a 16 year old female patient who underwent staged correction of her thoracolumbar scoliosis. A paravertebral catheter was inserted under direct vision for continuous infusion post operative analgesia following the anterior release. 48 hours after surgery a swelling was noted in the groin, which was confirmed with ultrasonography as a fluid collection. The swelling resolved upon removing the paravertebral catheter. This suggests that it was caused by the local anaesthetic fluid tracking along the psoas muscle. Retroperitoneal infections, venous thrombosis, femoral hernia, femoral artery aneurysm and inguinal lymphadenopathy are other differentials. Ultrasonography was a fast and sensitive investigation to rule out these differentials and determined that fluid communicating with the abdominal cavity was the cause for this swelling. The infused local anaesthetic had tracked down into the femoral triangle and the swelling resolved upon cessation of the infusion.