We have recently reported the application of RNAseq to mantle cell lymphoma (MCL) transcriptomes revealing recurrent mutations in NOTCH1. Here we describe the targeted re-sequencing of 18 genes mutated in this discovery cohort using a larger cohort of MCL tumors. In addition to frequent mutations in ATM, CCND1, TP53 and NOTCH1, mutations were also observed recurrently in MEF2B, TRAF2 and TET2. Interestingly, the third most frequently mutated gene was UBR5, a gene encoding a 2799aa protein, with multiple functions, including E3 ligase activity based on a conserved cysteine residue at the C-terminus. Non-synonymous mutations were detected in 18% (18/102) of tumors, with 61% of the mutations resulting in frameshifts in, or around, exon 58, predicted to result in the loss of this conserved cysteine residue. The recurrence and clustering of deleterious mutations implicate UBR5 mutations as a critical pathogenic event in a subgroup of MCL.