This paper explores the question how much detail a cost system needs to have in order to provide reliable cost information at a reasonable price. In general, fine-grained cost systems with a lot of detail (in product definition, in cost drivers and in cost pools) are expected to provide more reliable cost information than coarse- grained cost systems with less detail. This paper takes as an example the DBC cost system that has been developed for the Dutch hospital sector. The fine-grained DBC system with over 40,000 health care products appears to outperform lowergrained DRG systems with “only” 15,000 and 6,000 health care products on cost homogeneity and predictive validity. It does so however at the cost of a high number of products with measurement and specification errors, caused by a large number of outliers and by a low number of observations in product groups. The cost-effectiveness of the DBC system is not very high: only 3% of all DBC-codes explains 80% of total costs, whereas the lower-grained DRG system uses 14% of the codes to explain 80% of total costs. Combined with the high administration cost of the DBCsystem, it was from an economic perspective, a sensible idea to replace the finegrained DBC-system by the coarse-grained DOT system.