Objectives: B-cell acute lymphoblastic leukemia (B-ALL) is one of the most common leukemias affecting the pediatric population. It represents ~25% of cancer diagnoses among children. Specific genetic changes predict the prognosis in B-ALL with recurrent genetic changes. Here we present a case report of a 20-year-old male with B-ALL. The patient presented with acute onset worsening upper extremity pain with pallor, weight loss, dizziness, fatigue, and abnormal complete blood count (CBC). Conventional cytogenetics showed a karyotype of 46,XY,add(9)(q13),i(9)(q10)[19]. DNA FISH analysis performed on the bone marrow showed hemizygous deletion of the 9p21(CDKN2A) in 15.5% of the nuclei examined. The presence of an isochromosome 9q [i(9)(q10) is a rare event in pediatric B-ALL. An isochromosome 9q occurs in 0.6% of the patients studied in the literature. The significance of this abnormality in pediatric B-ALL is not clear. Profiling cases like this to understand the molecular mechanisms of rare chromosomal abnormalities and rare mutations in children with B-ALL could help us to better treat them., (Copyright© by the Association of Genetic Technologists.)