Chromosomal abnormalities resulting in deletion at 5q or monosomy 5 can occur in both acute myeloid leukaemia (AML) and myelodysplastic syndrome (MDS). Genes in the deleted region include NPM1, APC and CTNNA1. Deletions at 5q are also relatively common in therapy-related AML/MDS. These abnormalities can have diagnostic, prognostic, and therapeutic implications.