This is the first UK-based birth cohort study to look at teenage self-harm and suicidal thoughts and plans, and one of the largest studies internationally to examine these interrelationships in detail. Our results confirm previous findings that much adolescent self-harm, even where there was a desire to die, does not receive medical attention, emphasising the importance of community-based studies for providing information about prevalence. A key advantage of this study is the size and representativeness of the sample at the outset and the detailed prospectively recorded measures of socio-economic circumstances, development and mental health. The loss to follow up over the years may have led to selection bias, as those from the original sample who did not receive the questionnaire were more likely to be male and non-white, to have less than five GCSE/GNVQs at grades A*-C, and to have a mother in a manual social class, with lower educational qualifications, and with depressive symptoms when the individual was aged 11. Further, those who received the questionnaire but did not return it differed from respondents in similar ways. The results
