We report the case of a patient with myelodysplasia who had Sweet syndrome of the oral cavity. An atypical myeloid immunophenotype was present in the gingival biopsy specimen and in a concurrent bone marrow specimen. Fluorescence in situ hybridization performed on the gingival biopsy specimen demonstrated the same del(20q) cytogenetic abnormality present in the bone marrow, confirming the presence of a clonally related myeloid proliferation in both tissues. This is the first reported case of Sweet syndrome and myelodysplasia in which the chromosomal abnormality was identified in the neutrophilic infiltrate, confirming the neutrophilic infiltrate to be clonally related to the underlying myeloid neoplasm.