The risk of suicidal behaviour in major mood disorders is an inherent phenomenon and it strongly relates to the presence and severity of depressive episode. However, since the majority of mood disorder patients never commit or attempt suicide, special clinical characteristics of the illness as well as some personality, familial, psycho-social and demographic factors should also play a contributory role. Considering the clinically explorable suicide risk factors - discussed in this paper - in patients with major mood disorders, suicidal behaviour is predictable with a relatively good chance. As suicidal behaviour frequently develops later in the course of mood disorders, successful treatment of initially nonsuicidal major depressives and bipolar patients can prevent the later developing suicidal behaviour. This phenomenon could be called as "hidden suicide prevention". It means that preventing suicide is more easy than to predict it.