Criteria Did the study address a clearly focused issue? Was/were the study outcome(s) to be measured clearly described? Were the questions posed to assess outcome(s) clearly defined? Was the study samle clearly defined? Were participating schools recruited in an acceptable way? Were the pupils recruited in an acceptable way? 1 Were characteristics of subjects at enrolment reported? Is it clear how data were collected? Was participation rate reported? Was participation rate sufficiently high? Was the data analysis sufficiently rigorous? Were other factors accounted for that could affect outcomes?2 Were results appropriately reported? 3 Is there a clear statement of findings? Did the authors mention that the instrument used for data collection was pre-tested or validated? 8 Were the questions posed appropriate to address given outcomes? S 1 1 Y 15 15 14 13 4 11 12 15 10 9 7 15 15 15 11 1 1 1 6 1 1 4 1 2 4 Number of studies in each assessment category* N NC NR PR NP P Page 3 of 12 1 8 4 6 2 2 1 3 Samkange-Zeeb et al. BMC Public Health 2011, 11:727 http://www.biomedcentral.com/1471-2458/11/727 Table 1 Results of methodological assessment of studies included in the review *Y = Yes, S = Substandard, N = No, NC = Not Clear, NR = Not Reported, PR = Partially Reported, = Not Applicable, NP = Not Possible to Assess, P = Partly. 1 did all pupils at the school(s), respectively in the grade concerned, have the same chance to participate?. 2 for example, sex, age, grade, school type, social class. 3 were numbers of outcome events reported on?. conducted in Europe (Figure 1). A further 47 were excluded as they did not focus on knowledge and aware- ness of adolescents. Of the 25 identified articles dealing with knowledge on STDs among adolescents in Europe, 8 were excluded as they either did not specifically address the question of knowledge and/or awareness, or focused more on sexual behaviour/beliefs. A further seven articles were excluded because the study popula- tion was not clearly stated to be school-attending. A review of the references listed in the 10 articles meeting inclusion criteria yielded four additional rele- vant articles. One article reported on two studies, hence a total of 15 studies published from 1990-2000 were included in the systematic review. Six of the articles were published before the year 2000 [36-41], and nine after 2000 [42-49]. The studies report on surveys conducted from as early as 1986 to 2005 (Table 2). The majority of the 15 studies specifically focused on HIV/AIDS only (7 studies) [36,39,41,43,44,49], four on STDs in general [37,38,40,42], one on STDs in general with focus on HPV [47], and three on HPV only [45,46,48]. All the HPV studies were published after the approval and market introduction of the HPV vaccine in 2006. Generally the studies were conducted in particular regions/towns in different countries, with only one being conducted across three towns in three different countries (Russia, Georgia and the Ukraine) [43]. Six of the studies were conducted in Sweden [37,38,40,41,46,47] two in Russia [39,43] and one each in Ireland, [36] England, [42] Croatia, [44] Finland, [45] Italy [48] and Germany [49] (Table 2). In the studies, generally both male and female adoles- cents varying in age from 13-20 years were surveyed. One study surveyed females only [40] and adolescents 11-12 years old were included in only one study [49] (Table 2). Whereas most of the studies included assessed awareness and knowledge among boys and girls separately, only one study [48] specifically assessed the association between age and awareness/knowledge. Methodological summary of studies included in the review All studies included in the review were cross-sectional in design. Apart from one study which recruited pupils by mailing the questionnaire to all households with ado- lescents in the 9th grade, [45] pupils were recruited via schools. For 8 of the 15 studies it could not be deduced from the methods section how the participating schools were selected and in 4 studies it was not clear how the participating pupils were selected. The pupils completed questionnaires in school in 10 studies, and in two the questionnaires were completed at home [45,48].