TITLE. Biological and technical sources of variations in transcriptome sequencing of thyroid tissue AIM. To assess the effect of demographic, agonal and technical factors on whole-genome transcriptional variability of thyroid tissue using bulk RNASeq analysis (bioinformatics analysis). STUDY DESIGN. This research is designed as an exploratory research (in silica analysis). METHODS. The transcriptional variability of thyroid tissue was dissected by using RNAsequencing libraries from the Genotype-Tissue Expression project (v8 release). In total, 228 whole-genome expression profiles were analyzed in relation to their host demographics and sample attributes. Variance partition analysis, hierarchical clustering and matrix factorization were performed, followed by pathway enrichment profiling of highly expressed metagenes (Gene Ontology, Hallmark, Kyoto Encyclopedia of Genes and Genomes, Cell Signatures, Broad Molecular Signatures Database v7.4). RESULTS. Full blown Hashimoto’s thyroiditis, when present, was the dominant source of transcriptional variability. For healthy thyroid tissue, technical covariates outweighed the contribution from demographic data (age, sex, and ethnicity). Younger age, death on the ventilator, higher RNA integrity, short ischemia, and low autolysis were associated with an array of detoxifying and antioxidant defence genes from the NFR2 pathway. In contrast, older age, slow death, poor RNA integrity, long ischemia, and higher autolysis score were associated with transcriptional markers of vascular injury, hypoxic response, NFκB signalling, and fibroblast activation. CONCLUSIONS. Different patterns of transcriptional variability stemming from a broad range of demographic and technical covariates were identified. Many genes co-ordinately changed their expression, reflecting an ongoing transcription long after cessation of life.