To investigate sociodemographic and gender factors associated with suicide and suicide attempts among new users of antidepressants aged 75 and above.Register-based cohort study.National population-based cohort of Swedish residents aged ≥75 years.185 225 patients who initiated antidepressant medication between 1 January 2007 and 31 December 2013 were followed until 31 December 2014.Suicide and suicide attempts. Fine and Gray regression models were used to analyse the sociodemographic factors (age, country of birth, marital status, education level, last occupation, income and social allowance) associated with suicidal behaviours in the entire cohort and by gender.During follow-up, 295 suicides and 654 suicide attempts occurred. Adjusted sub-hazard ratios (aSHRs) for suicide were lower among older age groups (aSHR 0.73, 95% CI 0.53 to 0.99 for those 85-89 years; and aSHR 0.53, 95% CI 0.33 to 0.86 for those ≥90 years). A similar pattern was observed for suicide attempts. Suicide attempts were more common among those born in foreign countries (aSHR 1.58, 95% CI 1.16 to 2.15 for those born in another Nordic country; and aSHR 1.43, 95% CI 1.06 to 1.93 for those born in non-Nordic countries). In the gender-stratified analyses, being single or divorced, and born in another Nordic country was associated with a higher risk of suicide among men. Educational and occupational history and being born in a non-Nordic country influenced risk of suicidal behaviours in women.Suicidal behaviours occurred more commonly among new users who were 'younger' old adults and those with foreign background, suggesting that those groups might require greater support when initiating antidepressant therapy. Our findings suggest the need for gender-specific, multifaceted approaches to the prevention of suicidal behaviours in late life.