Objective: Chromosome 7 has been a focus of attention as a site harboring tumor suppressor genes whose loss of function contributes to leukemia transformation or tumor progression. Abnormalities of chromosome 7 are frequently encountered in primary and secondary MDS and AML and are usually difficult to determine because of the heterogeneity of breakpoints and their occurrence in complex karyotypes, which are difficult to analyze cytogenetically. Fluorescent in situ hybridization (FISH) analysis may be helpful in revealing the involvement of this chromosome in structural aberrations. Taking into consideration the sensitivity of this technique, it can also confirm the numerical aberrations of chromosome 7, even when they occur in small populations of cells. Because monosomy 7 and 7q deletion (–7/7q-) aberrations are considered as a poor prognostic factor in malignant myeloid disorders, establishing their presence is very important from the clinical point of view. Thus, the aim of the present work was to detect the molecular abnormalities of chromosome 7 (–7/7q-) in MDS and AML Egyptian patients and whether it has an implication on the prognosis of these diseases using the FISH technique.Subjects and Methods: Fluorescence in-situ hybridization was performed for chromosome 7 in a series of 30 patients: 20 patients diagnosed as AML (Group A) and 10 patients diagnosed as MDS (Group B) according to the FAB criteria.Results: Aberrations of Chromosome 7 were revealed in 26.6% of AML patients (Group A); While in group B (MDS patients); monosomy for chromosome 7 was the only abnormality detected and was found in 30% of cases.Patients who had normal FISH results showed a higher percentage (31.6%) of complete remission (CR) versus 0% in patients with monosomy or deletion who showed a higher percentage (100%) of death or showed a poorer response to therapy (NR). AML patients had a worse outcome when compared to MDS patients.In conclusion, Chromosome 7 abnormalities implicated worse prognosis in AML and MDS patients so they are more resistant to therapy, need more aggressive treatment and are more prone to relapse and death. So it is recommended to use FISH for detection of chromosome 7 abnormalities whenever possible due to its important prognostic value and hence clinical significance for better stratification of treatment modalities.