It has been accepted that the hypermutation status of immunoglobulin heavy chain genes (IgVH) is one of the most important independent prognostic factors in chronic lymphocytic leukemia (CLL). According to the degree ofIgVH hypermutaion, CLL patients can be stratified into prognostic groups. Given the impact ofIgVH mutation status on clinical setting, it has become highly desirable to standardize the laboratory methodologies used for IgVH mutation status determination. To check the reliability of our laboratory results, we performed a random interlaboratory testing. From 10 CLL samples tested, in 9 cases identical results were obtained in both laboratories. In one case, the result was discordant. The discrepancy was caused by theIgVH database used. This finding prompted us to double-check our cohort of 624 CLL patients, using IgBLAST and IMGT databases. The results showed 7.5% (47/624) discrepancies between both databases. In 21 out of 47 cases, the degree of hypermutation has changed in regard to the database used, resulting in major changes in the prognostic subgroup. Other irregularities between both databases were identified, with yet to be determined significance. In the light of presented data we would like to stress the necessity to identify/compile the most comprehensiveIgVH database to be used for the determination ofIgVH mutation status in CLL.