Background: Human papillomavirus (HPV) is the most common sexually transmitted agent worldwide and more than 100 types of HPV have been identified This systematic review was carried out to assess whether vaccinating boys with the same HPV vaccines currently offered to 11 to 12-year-old girls in Norway would be effective in preventing HPV-related diseases among males. The five included references represent two different clinical trials. The efficacy data is from one large randomized study that examined the effi cacy of prophylactic vaccination of males aged 16 to 26 with the quadrivalent HPV vaccine. Main findings: • This study shows that the quadrivalent vaccine is effi cacious in preventing external genital lesions, caused by infection with HPV 6, 11, 16 or 18, in males aged 16-26 (moderate quality of evidence). • Genital warts are the main type of genital lesions prevented by vaccinating males (moderate quality evidence). • Effect data on precancerous lesions such as penile intraepithelial neoplasia (PIN2+) resparse because of limited (three years) follow-up, and the results are not conclusive (low quality vidence).