Existing evidence on the association of telomere length with life expectancy and the risk of various age related diseases is discordant. This inconsistency in the data may be due to methodological factors, e.g., the differences in the techniques for measuring telomere length, cell harvesting, DNA isolation, and material. One of the general requirements to experiments concerned with the measurement of telomere length is the high quality of DNA samples under study. The current review considers the most common errors during the measurement of telomere length associated with the improper quality of the biological material.