Background: Teen pregnancy is associated with an array of negative social and health related outcomes for the mother as well as the baby. The risk of becoming a parent before the age of 20 is clearly elevated for former child welfare clients. Aim: The aim of this study is therefore to investigate the elevated birth rates among female adolescent child welfare clients by examining the relationship between contraceptive behaviour and pregnancies. Method: The study was based on a set of compiled register data. The study population were all females between the ages 14 and 19 during the years 2006-2008 (n. 487 115). The study group of main interest were child welfare clients who were compared to peers in the majority population as well as international and national adoptees. Analysis was conducted with multivariate logistic regression and the observed association was controlled for maternal, socio-demographic and behavioural factors. Results: The two sub-populations of child welfare clients both had much higher rates of retrieved hormonal contraceptives compared to the majority population, the international and the national adoptees up to age 17. In the ages 18 and 19 the rates were instead lower than the majority population. The child welfare clients had a stronger association to births than all groups of comparison, which was consistent with earlier research. All findings persisted after controlling for socio-demographic, maternal and behavioural factors. Conclusion: The child welfare clients showed a specific pattern of contraceptive behaviour over the age groups which was not consistent with the groups of comparison or with the expected relationship to birth rates. This suggests that teenage births cannot unanimously be predicted by the rates of retrieved hormonal contraceptives. The results imply that other factors than those investigated in this study are more influential regarding the contraceptive behaviour of this adolescent population.