BACKGROUND: The benefits of a health-related intervention may be compromised by the challenges of delivering the intervention on a large scale. We analyzed the process involved in the Tanzania National Voucher Scheme, a system for delivering insecticide-treated mosquito nets to pregnant women. We aimed to identify potential ways to equitably improve overall coverage of the intervention. METHODS: We defined five steps in the process. We collected data from a multistage cluster survey of nationally representative households conducted in 2007 across 21 districts in Tanzania. Using these data, we multiplied the rate of success of each step cumulatively to estimate the overall success of the system. RESULTS: The rate of coverage for use of insecticide-treated nets among pregnant women was 23% (95% confidence interval [CI] 19%-27%). We observed large differences in coverage by socio-economic status, from 7% (95% CI 4%-13%) among participants in the poorest households to 48% (95% CI 38%-59%) among those in the richest households. The rate of success of each step in the process was high (60%-98%). However, the cumulative rate of success for the process as a whole was low (30%). The largest and most inequitable reduction in coverage occurred in the step involving treatment of nets with insecticide. INTERPRETATION: The cumulative effect of modest attrition at several steps in the process substantially diminished the overall rate of coverage for all women, but most markedly among the poorest participants. Analysis of the process suggests that delivery of nets treated with long-lasting insecticide rather than untreated nets packaged with an insecticide-treatment kit could result in an improvement in coverage of 22 percentage points, from 30% to 52%.