We experienced a rare case of lipomyelomeningocele diagnosed at birth by magnetic resonance imaging which transformed the radiological appearance after 2 months into the transitional-type spinal lipoma with rapid increase in size of lipoma. Intraoperative findings revealed the presence of the dural sac extended dorsally outside the vertebral canal, which was characteristic of lipomyelomeningocele. Although there have been several reports showing that the size of spinal lipoma changed during development, there have been no reports which demonstrated alteration of radiological subtype with rapid increase of lipoma. Herein, we describe the first case of lumbosacral lipoma which changed radiological subtype from lipomyelomeningocele into transitional-type spinal lipoma.