Unlike in common melanocytic naevi, an acquired leukoderma (halo) surrounding a congenital melanocytic naevus is a rare phenomenon. A 6-year-old boy developed a depigmentation around a congenital melanocytic naevus on the right thigh. Simultaneously, segmental vitiligo appeared on the thigh, lower abdomen and buttock of the same side with sharp midline demarcation. Examination for associated autoimmune diseases proved negative. The simultaneous occurrence of a halo phenomenon around a congenital melanocytic naevus and segmental vitiligo, as well as identical histological and immunohistological findings in both pigmented lesions, suggest shared immunological mechanisms.