Retroperitoneal lymphangiomas are rare congenital vascular malformations. They cannot always be completely excised and are associated with high recurrence, complication and morbidity rates. We therefore utilize an alternative treatment concept in some cases. We excise the cystic types laparoscopically with a Nd: YAG laser (wavelength 1064 nm). Residual tissues are percutaneously managed by interstitial laser therapy under MRI monitoring. The high soft-tissue contrast of the MRI enables exact positioning of the laser fiber. The examination is thermosensitive and provides online and noninvasive demonstration of the interstitial tissue coagulation. We have treated four infants laparoscopically and three other children percutaneously.