Although whole-exome sequencing and whole-genome sequencing has tremendously improved our understanding of the genetic etiology of human disorders, about half of the patients still do not receive a molecular diagnosis. The high fraction of variants with uncertain significance and the challenges of interpretation of noncoding variants have urged scientists to implement RNA sequencing (RNA-seq) in the diagnostic approach as a high throughput assay to complement genomic data with functional evidence. RNA-seq data can be used to identify aberrantly spliced genes, detect allele-specific expression, and identify gene expression outliers. Amongst eight studies utilizing RNA-seq, a mean diagnostic uplift of 15% has been reported. Here, we provide an overview of how RNA-seq has been implemented to aid in identifying the causal variants of Mendelian disorders.“,”Although whole-exome sequencing and whole-genome sequencing has tremendously improved our understanding of the genetic etiology of human disorders, about half of the patients still do not receive a molecular diagnosis. The high fraction of variants with uncertain significance and the challenges of interpretation of noncoding variants have urged scientists to implement RNA sequencing (RNA-seq) in the diagnostic approach as a high throughput assay to complement genomic data with functional evidence. RNA-seq data can be used to identify aberrantly spliced genes, detect allele-specific expression, and identify gene expression outliers. Amongst eight studies utilizing RNA-seq, a mean diagnostic uplift of 15% has been reported. Here, we provide an overview of how RNA-seq has been implemented to aid in identifying the causal variants of Mendelian disorders.