A 26-year-old woman presented with asymptomaticbrownish plaques and a large red-brown tumour on theleft side of the abdomen (Fig. 1a). She reported havingbrown macules on this site since birth, which hadslowly enlarged during childhood (Fig. 1b) and adoles-cence, and which had been interpreted as a naevoidlesion by the family doctor. Six months before presen-tation to us, the lesion had changed its behaviour andnodules gradually developed.Physical examination showed three brown plaques,which were partially atrophic, and in some parts,subcutaneous nodules were palpable. On the lateralside of the lesion, there was a red-brown solid tumour,50 · 50 mm in size. Magnetic resonance imaging andan abdominal computer tomography showed a tumour47 · 47 · 30 mm in size, which approximated theabdominal musculature and pushed it backwards. Themusculature was not penetrated. No other abnormalit-ies were found.