Acute lymphoblastic leukemia (ALL) is the most common malignancy in children and is usually associated with numerical and struc- tural chromosomal changes. Although some of these changes are accepted as favorable or poor prognostic factors, the prognos- tic effects of others have not been well determined. In our study, we aimed to present the chromosomal changes in cases with child- hood ALL and their ratios in hematologic risk groups. Thirty four patients with childhood ALL were included in the study. Subjects were diagnosed with fluorescence in situ hybridization (FISH) analysis by using standard translocation, deletion and aneuploidy pro- bes. The chromosomal changes obtained from our analysis were classified into hematologic risk groups and their ratios were eva- luated. In our study, we found that the t(12.21) translocation was the most common abnormality in minimal and standard risk gro- ups, whereas the 9p21 deletion was the most common abnormality among high-risk patients. OZET Cocukluk Cai Akut Lenfoblastik Losemi'li Olgularda Molekuler Sitogenetik Bulgular Akut Lenfoblastik Losemi (ALL) cocukluk ca¤›nda gorulen en yayg›n malignite olup say›sal ve yap›sal kromozomal deifliklikler ile bir- likte gorulebilmektedir.Bu deiflikliklerin baz›lar›n›n iyi ya da kotu prognostik belirtec kabul edilirken baz›lar›n›n ise prognostik etkileri tam bilinmemektedir. Cal›flmam›zda, cocukluk ca¤› ALL vakalar›nda saptanan kromozomal deifliklikler ile hematoljik risk gruplar›n- daki oranlar›n› vermeyi amaclad›k. Cal›flmaya tan› alm›fl cocukluk ca¤› akut lenfoblastik losemili 34 olgu al›nd›. Olgulara, ALL ac›s›n- dan deer tafl›yan standart translokasyon, delesyon ve aneuploidi problar› kullan›larak floresan in situ hibridizasyon (FISH) analizleri yap›ld›. Saptanan kromozomal deifliklikler vakalar›n hematolojik risk gruplar›na gore s›n›fland›r›larak oranlar› deerlendirildi. Cal›flma- m›zda, 9p21 delesyonu yuksek riskli hastalar aras›nda en s›k gorulen anomali iken t (12.21) translokasyonu minimal ve standart risk grubunda en s›k gorulen anomali olduunu bulduk.