In clonality assessment in lymphoid malignancies expected size ranges of rearranged Ig/TCR PCR products are relevant and should be taken into account. Yet they should not be employed too strictly, as "undersized" and "oversized" products might still represent true rearrangement products. Now that Ig/TCR clonality testing has technically become relatively easy to perform in routine laboratories, correct interpretation becomes essential and preferably should be organized in close interaction between involved scientists.