We describe a patient with MDS/MPN with ring sideroblasts and thrombocytosis who had deletions of long arm of chromosome 5 (5q-) and chromosome 20 (20q-). Molecular studies showed an exon 9, frame shift mutation in the calreticulin (CALR) gene, and absence of mutations in JAK2, MPL, SETBP1 or SF3B1. Treatment with lenalidomide resulted in durable clinical remission which has lasted 2 years.