The results of a systematic review of the international literature on the prevalence of suicidal phenomena in adolescents, including the influence of survey method, gender, and ethnicity are reported. The literature was searched using six electronic databases to identify all population-based studies of self-reported suicidal phenomena; 128 studies were included, comprising 513,188 adolescents. The mean proportion of adolescents reporting they had attempted suicide at some point in their lives was 9.7% (95% CI, 8.5–10.9), and 29.9% (95% CI, 26.1–33.8) of adolescents said they had thought about suicide at some point. Females were significantly more likely than males to report most suicidal phenomena. A lower prevalence of some suicidal phenomena was found for Asian populations. The prevalence of suicidal phenomena varied depending on the terminology used and tended to be higher in studies employing anonymous questionnaires than in studies employing non-anonymous methods (questionnaires or interviews), although most of these differences were not statistically significant.