BACKGROUND: Smegma is widely believed to cause penile, cervical and prostate cancer. This nearly ubiquitous myth continues to permeate the medical literature despite a lack of valid supportive evidence. METHODS: A historical perspective of medical ideas pertaining to smegma is provided, and the original studies in both animals and humans are reanalysed using the appropriate statistical methods. RESULTS: Evidence supporting the role of smegma as a carcinogen is found wanting. CONCLUSIONS: Assertions that smegma is carcinogenic cannot be justified on scientific grounds.