The emergence of suicidal ideation and suicide-related behaviour in patients receiving drug treatment is of concern because of the overall burden of these conditions and the possible link with completed suicide. Observational studies have been useful in generating hypotheses of causality but are confounded by the association between various disease states and increased suicide-related behaviour and completed suicide. The demonstration of causality requires experimental studies, especially randomised controlled trials, and meta-analyses. Unfortunately, the lack of uniform requirements for defining, detecting and recording suicidal ideation, suicide-related behaviour and completed suicide creates difficulties in comparing studies. Nevertheless, there is evidence of an association between SSRIs and other newer antidepressant drugs and treatment-emergent suicidal ideation and suicide-related behaviour in both children and adults; however, an increase in completed suicide as a result of treatment with SSRIs and other newer antidepressant drugs has not been demonstrated. Atomoxetine has also been associated with treatment-emergent suicidality, based on the results of a meta-analysis. Although similar associations have been proposed for some antiepileptic drugs, isotretinoin and interferon-alpha, they are yet to be supported by evidence from randomised controlled trials or meta-analyses.