We investigated the impact of time interval, primary vs. metastatic biopsy site, variant allele fraction (VAF) and histology on concordance of KRAS alterations in tissue vs. circulating tumor DNA (ctDNA), and association of concordance with survival. Blood and tissue were evaluated by next-generation sequencing in 433 patients with diverse cancers. Altogether, 101 patients (23.3%) had KRAS alterations: 56, ctDNA (12.9%); 81, tissue (18.7%); and 36, both (8.3%). The overall blood and tissue concordance rate for KRAS alterations was 85%, but was mainly driven by the large negative/negative subset. Therefore, specificity of one test for the other was high (88.1-94.3%), while sensitivity was not high (44.4-64.3%) and was lower still in patients with >6 vs. ≤2 months between blood and tissue sampling (31.0-40.9% vs. 51.2-84.0%; p = 0.14 time interval-dependent sensitivity of blood for tissue; p = 0.003, tissue for blood). Positive concordance rate for KRAS alterations was 57.1% vs. 27.4% (colorectal vs. noncolorectal cancer; p = 0.01), but site of biopsy (primary vs. metastatic) and VAF (%ctDNA) was not impactful. The presence of KRAS alterations in both tests was independently associated with shorter survival from diagnosis (hazard ratio, 1.72; 95% confidence interval, 1.04-2.86) and from recurrent/metastatic disease (1.70; 1.03-2.81). Positive concordance of KRAS alterations between ctDNA and tissue was negatively affected by a longer time period between blood and tissue sampling and was higher in colorectal cancer than in other malignancies. The presence of KRAS alterations in both tests was an independent prognostic factor for poor survival.