We investigated a 4-year-old Japanese boy with oculocutaneous albinism who had a solitary pigmented mole measuring 5 mm in diameter on his back. An electron microscopic tyrosine incubation test and a DOPA reaction test clearly demonstrated the presence of tyrosinase activity in the patient's hypopigmented skin. The presence of tyrosinase activity was confirmed by tests on hair bulb samples. Histopathological evidence showed that the mole was a typical compound cellular naevus with melanin pigmentation. Although no reports to date have focused on the relationship between pigmented naevi in albinism and tyrosinase activity, our findings suggest that the occurrence of pigmented naevi in an albino may indicate the presence of tyrosinase activity.