OBJECTIVE To compare demographic and psychosocial characteristics of completed suicide between younger and older adolescents, and by sex. METHODS Data was collected from the Victorian Suicide Register, which contains information on suicides reported to the Coroners Court of Victoria. RESULTS Between 2006 and 2015, there were 273 completed suicides aged 10-19 years, with none aged 10-12 years. There were 171 (63%) suicides in the older adolescent group (17-19 years), and 102 (37%) in the younger group (13-16 years). Males comprised 184 cases (67%) and females 89 (33%). A higher proportion of both younger and female adolescents had experienced abuse, peer conflict and bullying. There was also a higher incidence of previous self-harm in younger and female adolescents. Older adolescents were more likely to not be in formal education, employment or training. CONCLUSIONS Suicide in younger adolescents and females appear to share characteristics, and differ from older and male adolescents. Negative interpersonal relationships and previous self-harm with possible co-existenting mental illness appear to be key differentiating features. Implications for public health: Understanding completed suicide is an important step towards prevention, and our results suggest a need for developmentally and sex-specific suicide prevention strategies.