The survival of patients with myelodysplastic syndromes is strongly affected by chromosomal abnormalities. Patients with an isolated del(5q31) have a favourable prognosis that worsens with the addition of another chromosomal abnormality. It has been reported that both patients with isolated del(5q31) and those with one single additional chromosomal abnormality achieve hematological and cytogenetic remissions with lenalidomide therapy. Whether this translates into improved overall survival of the patient population is unclear. We analysed data of 25 patients with myelodysplastic syndrome and complex chromosomal abnormalities including del(5q31) and show that their median survival is between 7 and 8 months, irrespective of the medullary blast count. Furthermore, we present data of a patient with complex karyotypic anomalies inclusive of del(5q31) treated with lenalidomide who achieved complete cytogenetic remission. This cytogenetic remission was diagnosed after 6 months, and the hematological response is ongoing at 9 months of therapy at a dose of 5 mg p.o. daily. We conclude that lenalidomide has the potential to induce sustained hematological and cytogenetic remissions in the poor prognosis MDS subgroup of del(5q31) patients with complex chromosomal anomalies and that this is likely to improve overall survival.