T-cell prolymphocytic leukemia (T-PLL) is a rare and aggressive subtype of chronic lymphocytic leukemia. Usually it presents in older people with a median age of 61 years. T-PLL is characterized by elevated white blood cell (WBC) count with anemia and thrombocytopenia, hepatosplenomegaly, and lymphadenopathy; less common findings are skin infiltration and pleural effusions. The most frequent chromosomal abnormalities in T-PLL include 14q11.2, chromosome 8, and 11q rearrangements. Also deletions in the short arm of a chromosome 9 are reported in ~30% of T-PLL together with other aberrations. Here we report a childhood T-PLL case with a de novo del(9)(p13) as sole acquired anomaly leading to monosomy of the tumor suppressor gene CDKN2A (cyclin-dependent kinase inhibitor 2A). Also, to the best of our knowledge this is the first case of a childhood T-PLL with this aberration.