To assess the cost-effectiveness of hepatitis C virus treatment with pegylated interferon alfa-2a and ribavirin in current and former people who inject drugs (PWID).A decision analytic model simulated the lifetime costs and outcomes of four treatment options: early treatment with mild fibrosis, standard treatment with moderate fibrosis, late treatment with compensated cirrhosis, and no treatment. Treatment modalities were simulated across current, former, and never-injector cohorts of 1000 hypothetical patients with chronic hepatitis C virus. The main outcome measures were incremental costs ($AUD) per quality-adjusted life years (QALYs) gained, and incremental cost-effectiveness ratios (ICERs) were calculated for each cohort.Treatment of current PWID during mild fibrosis resulted in a discounted average gain of 1.60 QALYs (95% confidence interval 0.93-2.26) for an added cost of $12,723 ($11,153-$14,396) compared with no treatment, yielding an ICER of $7941 per QALY gained ($6347-$12,017). Former PWID gained 1.80 QALYs (1.29-2.33) for $10,441 ($8843-$12,074) for early treatment compared with no treatment, resulting in an ICER of $5808 per QALY gained ($5189-$6849). Never-injectors gained 2.33 QALYs (1.87-2.80) for $9290 ($7642-$10,912) compared with no treatment-an ICER of $3985 per QALY gained ($3896-$4080). Early treatment was more cost-effective than late treatment in all cohorts.Despite comorbidities, increased mortality, and reduced adherence, treatment of both current and former PWID is cost-effective. Our estimates fall below the unofficial Australian cost-effectiveness threshold of $AUD 50,000 per QALY for public subsidies. Scaling up treatment for PWID can be justified on purely economic grounds.