There is a lack of specific knowledge about the dose–response effect of multiple parental risk factors for suicide attempts among children and adolescents. The aim of this study was to determine the dose–response effect of multiple parental risk factors on an offspring's risk for suicide attempt.

We designed a population-based two-generation nested case–control study and used Danish register data. A population of 403 431 individuals born between 1983 and 1989 was sampled. Among these, 3465 (0.8%) were registered as having had a suicide attempt. Twenty controls were matched to each case and a link to the offspring's biological parents was established.

There was a dose–response relationship between the number of exposures and the risk of suicide attempts, with the increased risk seeming to be a multiplicative effect. Parental suicide, suicide attempt, psychiatric illness and low level of income were all significant independent risk factors for offspring's suicide attempts.

Knowledge of the effect of multiple risk factors on the likelihood of suicide attempts in children and adolescents is important for risk assessment. Dose–response effects of multiple parental risk factors are multiplicative, but it is rare for children and adolescents to be exposed to multiple parental risk factors simultaneously. Nevertheless, they should be considered along with the offspring's own multiple risk factors in determining the overall risk of a suicide attempt. Further research incorporating both parental and offspring's risk factors is indicated to determine the overall dose–response effect of multiple risk factors.