Although tissues in the case series of anal, penile, vaginal and vulvar neoplasms that have looked for evidence of HPV infection by probing for HPV DNA have been selected for convenience, they support the view that HPV, especially type 16, is associated with approximately 50% of these tumours. A higher percentage of the anal, vaginal and vulvar tumours are associated with HPV 16 than are penile tumours. This discrepancy may be due to the low number of penile tumours studied or to a true difference in the proportion of penile cancer cases related to HPV. HPV 6/11 and 18 are found less frequently at all anatomic sites. About 10% of tumours that are probed for these viruses are positive, although there are some notable exceptions such as a study that found 39% of penile tumours positive for type 18 and a study that found approximately two thirds of vulvar tumours positive for HPV 18 using Southern blot hybridization. For all of these tumours, there is likely to be a subset of the cases who develop their cancer through mechanisms that do not involve HPV. The case-control studies found a strong association with genital warts, number of sexual partners and, with the exception of vaginal cancer, smoking and/or heavy smoking at the time of diagnosis of the disease. A history of genital warts, smoking at diagnosis, and seropositivity to HSV2 are exposures that have also been found to be associated with cervical cancer. A population-based case-control study in western Washington and Vancouver, British Columbia that studied all anogenital cancers found that a history of genital warts was stronger among patients with vulvar, anal, vaginal and penile cancer than among those with cervical cancer. This was also true of smoking at diagnosis, with the exception of vaginal cancer, where there was little excess risk. This study and other supporting data indicate that these anogenital tumours share many of the same risk factors as cervical cancer.