Epidermal naevus syndrome was first described by Solomon et al. in 1968, based on a study of 12 patients. Herein we report the case of a 20-year-old female diagnosed with epidermal naevus syndrome at the age of 3 years. Subsequently she experienced several different symptoms and at the last exploration a suspicious lesion was found in her bladder. The definitive pathology diagnosis was transitional cell carcinoma of the bladder, which is extremely rare in patients aged <21 years. It seems that this neoplastic lesion was directly related to the essential pathology of the patient, namely epidermal naevus syndrome.