Recent claims-based analyses of health care utilization,particularly in the inpatient setting, have suggested anarrowing of the risk difference for stone disease betweenmen and women [2,3]. Our data show that the overallprevalence of stone disease is 10.6% in males and 7.1% infemales. At least two potential explanations exist for theseapparently contradictory findings. First, these differentfindings could represent gender-based practice variation;that is, for reasons that are not illuminated by these data,men may be less likely to be treated as inpatients for stonedisease. Alternately, our data are potentially consistent withthe hypothesis that in the past, men were much more likelyto form stones (represented by the large difference inprevalence between males and females aged 50 yr), butrisks are currently more equal, as represented by the verysimilar prevalence of stone disease among males andfemales aged 20–49 yr. Because of the cross-sectionalnature of the NHANES dataset, it is difficult to conclusivelytest this hypothesis. The NHANES dataset is specificallydesigned to estimate the prevalence of conditions in the USpopulation and should be considered more reliable thanclaims-based utilization data for addressing questions ofdisease prevalence.