p16 is a tumour-suppressor gene located on chromosome 9 and it is one of the cyclin-kinase inhibitors (CKIs) which binds specifically to cdk4 and cdk6 , thus halting cell cycle progression from G1 to S phase.The aim of work is detection of aberrant p16 methylation by methylation-specific PCR in adult and childhood acute leukaemias and to investigate its role in pathogenesis & clinical outcome of the disease.The study included thirty newly diagnosed cases, 17 were ALL and 13 were AML cases. In this study, 35% of ALL and 31% of AML cases had methylated p16 promoter, its incidence in T-ALL phenotype being more than that in B-ALL phenotype, which was reported in previous studies. Although there was no statistically significant difference between cases with methylated and unmethylated p16 as regards outcome of 2 months’ therapy, yet 66% and 100% of these cases had a bad prognosis in ALL & AML respectively. AML cases with methylated p16 were significantly younger than ALL cases.MSP is suitable for this assay, being both sensitive and specific. The study should be applied to a larger study group and with a longer follow-up interval.