Introduction: Total (-7) or partial (7q-) monosomy 7 is the second frequent abnormality in MDS, occurring in around 12% of MDS/AML and up to 40% of therapy-associated MDS/AML. The present study was designed to analyze clinical features, prognosis and response to different therapeutic strategies in patients with -7 or del(7q) in a multicentric, retrospective cohort study. Patients and Methods: 471 patients with MDS/AML following MDS and monosomy 7 were registered and retrospectively analyzed. The median observation time was 3.6 years. Inclusion criteria were defined as follows: Morphologic diagnosis of MDS/AML following MDS, bone marrow blast count Results: 147 patients (31.2%) showed 7q-, 313 (66.5%) -7 and 11 (2.3) patients showed both abnormalities at the first cytogenetic examination. The abnormality was detected by CBA±FISH in 440 (93.4%) and by FISH only in 31 (6.6%). In the latter cases, the CBA was either unsuccessful or showed a normal karyotype. In 182 (38.6%) patients, -7/del7q was detected as a single abnormality, 77 (16.3%) showed two abnormalities and 184 (39.1%) showed a complex karyotype involving -7/7q-. As previously described (Schanz et al., 2012), untreated patients with an isolated 7q- as compared to an isolated -7 show a better prognosis regarding OS (median: 4.0 vs. 0.7 years; p Conclusions: To our knowledge, the study describes the largest patient cohort with MDS/AML and monosomy 7 published to date. Further data regarding the clinical characteristics of this subgroup of patients and the treatment regimes applied will be presented in detail. The study was supported by research funding from Celgene Disclosures Schanz:Celgene: Honoraria, Research Funding, Travel grants: Celgene, Novartis, Lilly Other. Gotze:Celgene Corp, Novartis Pharma: Honoraria. Nolte:Celgene, Novartis: Membership on an entity9s Board of Directors or advisory committees, Research Funding, Travel grants Other.