The development of commercial reagents designed specifically for use with formalin-fixed paraffin-embedded (FFPE) tissue has unlocked the diagnostic potential of this prolific resource. The availability of archival FFPE tissue and tissue from current patients make it an ideal resource for molecular testing. Despite its stability and ability to preserve morphological information, FFPE provides a number of technical challenges to the study of biomolecules. In particular, the cross-linking and processing present problems in the extraction and isolation of DNA, RNA and protein and affect their use in downstream analysis. Here we will discuss some of the problems of FFPE tissue, how they can be overcome and how FFPE material can be used within clinical molecular diagnostics.