The omission of complete exons in a proportion of mature transcripts has been shown for a variety of genes. In the case of the cystic fibrosis transmembrane conductance regulator gene, this phenomenon has previously been observed for exons 4, 9 and 12. Here, we describe the detection of a combined skipping of exons 11 and 12 in the absence of detectable transcripts missing only exon 11. This constellation has been found both in peripheral blood cells and in specifically expressing lung tissue, and excludes the possibility that the simultaneous skipping of both exons is merely a stochastic combination of single exon skipping events.