Chronic myelogenous leukemia (CML) is caused by the BCR‐ABL1 fusion gene that encodes for a constitutively‐active tyrosine kinase. Adults and children with CML are typically treated with imatinib mesylate, a BCR‐ABL1 tyrosine kinase inhibitor (TKI), or a second‐generation TKI. Several case reports have documented growth delay of unknown mechanism in children with CML treated with imatinib. We report a seven‐year‐old identical twin with CML who developed significant growth delay, as compared to her twin, during five years of TKI therapy. Detailed endocrine evaluation showed acquired growth hormone deficiency, a pathway potentially inhibited by TKIs. Pediatr Blood Cancer 2011;56:671–673. © 2010 Wiley‐Liss, Inc.