OBJECTIVES: Antidepressants carry an increased risk of suicidality in children, adolescents and young adults.  The primary aim was to determine antidepressant prescribing and cost to patients aged 18 years and younger in a South African private health care sector patient population. METHODS: A retrospective, cross-sectional pharmacoepidemiological study was undertaken on prescription data of a private pharmacy group in South Africa for 2009.  The study focused on antidepressant prescribing.  No diagnoses were available.  A total of 814540 antidepressants were prescribed, of which 12549 were prescribed to patients aged 18 years or younger. RESULTS: A total of 4269 patients (53.74% females) received an average of 2.94 (SD = 3.31) antidepressants over the year.  The total cost of antidepressant prescribing was R1 581480, with an average cost of R126.02 per product (item).  Two-thirds (66.67%) of antidepressants were prescribed to patients from 12 to 18 years of age.  Selective serotonin re-uptake inhibitors (SSRIs) accounted for 55.91% of antidepressant prescribing, followed by tricyclic antidepressants (32.32%), together accounting for 79.49% of antidepressant cost.  Lithium was only prescribed to 1.04% of patients in this age group.  The highest average cost was for serotonin and noradrenaline re-uptake inhibitors (R322.94 per product), selective mono-amine oxidase inhibitors (R177.20) and SSRIs (R155.52).  Tablets were the preferred dosage form.  The most frequently prescribed active ingredients were imipramine (19.77%), escitalopram (14.60%), citalopram (14.09%) and fluoxetine (13.92%), together accounting for 62.38% of prescribing frequency. CONCLUSIONS:   Diagnoses were not available, therefore only prescribing trends could be investigated.  Fluoxetine generally has a favourable risk-benefit balance (prescribed “off label”), yet it only had a prescribing frequency of 13.92% in this study.  Active ingredients such as escitalopram and citalopram are not preferable in this age group.  The risk of prescribing antidepressants in children, adolescents and young adults should be balanced against the clinical need.