Single nucleotide polymorphism array (SNP‐A) analyses are increasingly being introduced in routine genetic diagnostics of acute lymphoblastic leukemia (ALL). Despite this, only few studies that have compared the diagnostic value of SNP‐A with conventional chromosome banding have been published. We here report such a comparison of 296 ALL cases, the largest series to date. Only genomic imbalances >5 Mb and microdeletions targeting the BTG1, CDKN2A/B, EBF1, ERG, ETV6, IKZF1, PAX5, and RB1 genes and the pseudoautosomal region 1 (PAR1) were ascertained, in agreement with recent guidelines. Of 36 T‐cell ALL cases, the karyotypes of 24 cases (67%) were revised by SNP‐A analyses that either revealed additional imbalances >5 Mb or better characterized the changes found by G‐banding. Of 260 B‐cell precursor (BCP) ALL cases, SNP‐A analyses identified additional copy number alterations, including the above‐mentioned microdeletions, or better characterized the imbalances found by G‐banding in 236 (91%) cases. Furthermore, the cytogenetic subtype classification of 41/260 (16%) BCP ALL cases was revised based on the SNP‐A findings. Of the subtype revisions, 12/41 (29%) had clinical implications as regards risk stratifying cytogenetic groups or genotype‐specific minimal residual disease stratification. We conclude that SNP‐A analyses dramatically improve the cytogenetic characterization of both T‐cell and BCP ALL and also provide important information pertinent to risk stratification of BCP ALL.