A 42-year-old man had a large speckled lentiginous nevus on the left side of his trunk. The involved area was painful when touched and paresthetic. Moreover, the ipsilateral half of his body showed a pronounced hyperhidrosis. This case can be categorized as a typical example of speckled lentiginous nevus syndrome, a recently recognized phenotype characterized by a speckled lentiginous nevus of the papular type and ipsilateral neurological abnormalities in the form of dysesthesia, muscular weakness or hyperhidrosis. Speckled lentiginous nevus syndrome represents a mosaic phenotype. Most likely it originates from loss of heterozygosity occurring in a heterozygous embryo at an early developmental stage.