During chromosome analysis the finding of few cells with X-chromosome aneuploidy in a phenotypically normal woman is not unusual - so-called low-grade mosaicism for X aneuploidy (LLX-A). Such results can be difficult to interpret. In this review, LLX-A and its clinical implications are discussed, and based on the current literature it can be concluded, that LLX-A is an age-related phenomenon not related to reproductive issues such as recurrent abortions. This should be taken into account in any laboratory performing chromosome analysis.