Repeated biopsies of a large pigmented lesion of the scalp of a young boy over a six-year period showed the characteristic features of a cellular blue nevus. Recent severe neurologic symptoms necessitated more radical surgical intervention. This disclosed focal invasion of the underlying skull, meninges, and brain. Apart from focal necrosis and multiple nucleoli in the most recent surgical specimen, the histologic features of the lesion have remained constant, despite its locally aggressive behavior. Electron microscopic studies demonstrated distinctive nucleolar configurations not previously reported.