The spread of electronic use of data in various areas has put importance of data quality to higher level. Data quality has syntactic and semantic component; the syntactic component is relatively easy to achieve if supported by tools (either off-the-shelf or our own), while semantic component requires more research. In many cases such data come from different sources, are distributed across enterprise and are at different quality levels. Special attention needs to be paid to data upon which critical decisions are met, such as medical data for example. The starting point for research is in our case the risk of the medical area. In the paper we will focus on the semantic component of medical data quality.