Next-generation sequencing (NGS) is routinely used for constitutional genetic analysis. However, cross-contamination between samples constitutes a major risk that could impact the results of the analysis. We have developed ART-DeCo, a tool using the allelic ratio (AR) of the Single Nucleotide Polymorphisms sequenced with regions of interest. When a sample is contaminated by DNA with a different genotype, unexpected ARs are obtained, which are in turn used for detection of contamination with a screening test, followed by identification and quantification of the contaminant. Following optimization, ART-DeCo was applied to 2222 constitutional DNA samples. The screening test was positive for 191 samples. In 33 cases (contamination percentages: 1.3% to 29.2%), the contaminant was identified and was mostly located in adjacent wells. Three other positive cases were due to barcoding errors or mixture of two DNA samples. Interestingly, the last contaminated sample corresponded to a bone marrow transplant recipient. Lastly, no contaminant was identified in 154 weakly positive ( < 4%) samples that were considered to be irrelevant to constitutional genetic analysis. ART-DeCo lends itself to mandatory quality control procedures, also highlighting the delicate steps of library preparation, resulting in practice improvement. Importantly, ART-DeCo can be implemented in any NGS workflow, from gene panel to genome-wide analyses. https://sourceforge.net/projects/ngs-art-deco/ .