The aim of this study was to provide an incremental cost-effectiveness analysis comparing intravenous immunoglobulin (IVIg) and prednisolone treatment for chronic inflammatory demyelinating polyradiculoneuropathy. Patients were recruited to a double-blind randomized crossover trial from nine European centres and received either prednisolone or IVIg during the first 6-week treatment period on which the economic evaluation was based. A societal perspective was adopted in measuring service use and costs, although the costs of lost employment were not included. The main outcome measure in the economic evaluation was the number of quality adjusted life years (QALYs) gained, with change in a 11-point disability scale used to measure clinical outcomes. Service use and quality of life data were available for 25 patients. Baseline costs were controlled for using a bootstrapped multiple regression model. The cost difference between the two treatments was estimated to be euro 3754 over the 6-week period. Health-related quality of life, as measured by the EuroQol EQ-5D instrument, increased more in the IVIg group but the difference was not statistically significant. Using a net-benefit approach it was shown that the probability of IVIg being cost-effective in comparison with prednisolone was 0.5 or above (i.e. was more likely to be cost-effective than cost-ineffective) only if one QALY was valued at over euro 250 000. The cost-effectiveness of IVIg is greatly affected by the price of IVIg and the amount administered. The impact of later side-effects of prednisolone on long-term costs and quality of life are likely to reduce the cost per QALY of IVIg treatment.