Cost-effectiveness and cost-utility analyses of immunisation strategies against invasive Haemophilus influenzae type b (Hib) disease in Australia were based on a hypothetical birth cohort of 250,000 non-Aboriginal Australian children. The model predicted that, without immunisation, 625 cases of invasive Hib disease would occur in under-five-year-olds, with direct costs of $10.2 million. Universal public sector vaccination beginning before six months of age (6MVAC) prevented 80 per cent of cases; vaccination at 12 months (12MVAC) 62 per cent and at 18 months (18MVAC) 46 per cent. At a vaccine cost of $15 per dose, 18MVAC gave the lowest cost per quality-adjusted life year (QALY) over a wide range of model assumptions, with 6MVAC the 'best' alternative. The best estimate ($ per QALY) for 6MVAC was $6930 (three doses), for 12MVAC $9136 (two doses) and for 18MVAC $1231 (one dose). The cost per QALY of single dose catch-up immunisation of older children was estimated at $8630 at two years, $27,000 at three years and $117,000 at four years if done at a scheduled visit; these values were increased if an additional medical visit was included. The threshold cost per vaccine dose at which an immunisation program became cost-saving was estimated for 6MVAC, 12MVAC and 18MVAC as $11, $10 and $14. Even under a worst-case scenario, an immunisation program at 6, 12 or 18 months became cost-saving if indirect costs of death were included. Comparison with previous analyses revealed the importance of the incidence and age distribution of disability and assumptions about vaccine administration costs in determining model outcomes.