A 68-year-old female patient had been treated locally and systemically for onychomycosis of the left thumbnail for 1 year. During the course of treatment there was increasing destruction of approximately 50% of the nail without Hutchinson's sign. Dermoscopically there were yellow to brown vertical stripes of varying width in the remaining parts of the nail. In the visible nail matrix reddish, brownish and grey-black colored components with varying differential structures could be detected. An acrolentiginous melanoma with a diameter of 1.04 mm could be identified histologically and the associated onychomycosis was confirmed by culturing.