AIMS: To demonstrate an application of health economic principles in histopathology by using the sampling of transurethral resections of prostate specimens. By demonstrating how marginal costs are calculated the aim is to illustrate that the potential opportunity cost of sampling entire specimens is much greater than would be anticipated by taking average cost, or the cost of producing a histological section alone. METHOD: A mathematical model is used with data obtained from the Aberdeen pathology department files and published estimates of the likely percentage of cancerous chippings in each specimen. RESULTS: The average cost of each cancer detected remains low, between 47 Pounds and 151 Pounds, in all the scenarios examined. However, the marginal costs can become high, exceeding 10,000 Pounds in larger specimens, if all the chippings are processed. CONCLUSIONS: This study demonstrates that there are potential opportunity cost penalties to histopathological services associated with sampling strategies. Although the results are derived from a hypothetical mathematical model using local data that applies only to histopathology, the method could be widely applied. The principles of marginal analysis should be performed by multidisciplinary teams and include outcomes as well as a broader range of costs, including those that arise subsequent to diagnosis.