The HPV types that cause cervical cancer are sexually transmitted, but there is little evidence that infection can be avoided by behavioural changes, such as condom use. In contrast, prophylactic vaccines against HPV infection are likely to have high efficacy. In principle, the effectiveness of HPV vaccination as a strategy for cervical cancer control can be measured either by monitoring secular trends in cervical cancer incidence or by conducting randomized trials. The former approach is unlikely to provide convincing evidence of effectiveness, since cervical cancer rates are subject to strong secular trends that are independent of intervention measures. A few phase III trials of HPV prophylactic vaccines are now being started. Such trials are very expensive studies involving frequent and complicated investigations. It is important, however, to start as soon as possible simpler trials designed to demonstrate the effectiveness of HPV vaccine in field conditions, i.e. in developing or intermediate countries which suffer the major burden of mortality from cervical cancer. Such trials may capture a difference in the most severe, and rarest, preinvasive cervical lesions (i.e., the real target of any HPV vaccine) over a prolonged follow-up (20 years at least). The design of such studies is briefly considered for two areas: Southern India and South Korea. This paper is available at: http://www.insp.mx/salud/index.html.