Dissimilarities in the approaches used to certify or code underlying causes of death may diminish the usefulness and reliability of cause-of-death statistics. Consistency of cause-specific mortality data within a given country can be regarded as one of the criteria for evaluating data quality. In the present paper, we assess the subnational consistency of cause-of-death statistics in four countries: Russia, Germany, the U.S., and France. We estimate the shares of major groups of causes in the mortality structures of subnational entities (regions), and compare them with the inter-regional average values. Next, we visualize the deviations on heat map matrices. This allows us to pinpoint the cases that deviate the most with respect to regions and causes of death, as well as the causes with high levels of within-country variability, and the regions with unique mortality structure. Among the countries that we examined, France has the most consistent cause-of-death data across its regions, while Russia has the largest number of outliers. We also found that causes of death that do not have strict diagnostic criteria (e.g., ill-defined) tend to display higher variability, while the shares of causes that are easier to diagnose as underlying are more stable across the regions.