OBJECTIVE: To investigate sociodemographic variation in antidepressant utilisation. DESIGN AND SETTING: Cross-sectional analysis of antidepressant prescription under the Pharmaceutical Benefits Scheme in Australia, 2003-2005. MAIN OUTCOME MEASURES: Antidepressant utilisation (defined daily dose/1000/day) by sex, age, socioeconomic status (SES) and geographical area. RESULTS: Total antidepressant utilisation increased with age. Among those aged > or = 15 years, female utilisation was about double that of males. About half of antidepressant utilisation was accounted for by sertraline, venlafaxine, citalopram, and paroxetine. SES differentials in antidepressant utilisation changed across age groups for males and females: among those aged < or = 19 years, total antidepressant utilisation was significantly less in lower SES groups (P < 0.001); there was no relationship to SES among 20-29-year-olds; and among those aged > or = 30 years, antidepressant utilisation was significantly higher in lower SES groups (P < 0.001). SES differences were attenuated after adjusting for urban or rural residence, but remained statistically significant. Antidepressant utilisation rates were highest in regional centres. CONCLUSION: Antidepressant utilisation in Australia partially reflects sociodemographic differences in the prevalence of affective disorder. Discrepancies between treatment provision and treatment need suggest that not all social strata in Australia have equal access to these treatments.