Imatinib (Gleevec®/Glivec®) has demonstrated high and durable hematologic and cytogenetic response rates, favorable safety and toxicity profiles, and prolonged survival when used for the treatment of chronic myeloid leukemia (CML). Imatinib copy drugs are currently available in some countries; however, the safety and efficacy of these compounds have not been widely assessed. We present a patient who received the copy drug imatinib-COPER, lost hematologic response while on therapy, and was subsequently treated with branded Glivec. This report, and other published cases, suggests that imatinib copy drugs may not be equivalent to branded Glivec in pharmacology, safety, and efficacy. The case was a 42-year-old Moroccan male with CML. Initial therapy with hydroxyurea alone followed by hydroxyurea in combination with interferon-α resulted in durable complete hematologic remission (CHR). Due to adverse effects, the patient was switched to imatinib-COPER at 400 mg/day. Despite compliance with therapy, he lost his CHR after 2 years and presented with aplasia requiring a blood transfusion. Administration of Glivec in combination with hydroxyurea resulted in re-achievement of complete hematologic remission that was stable at last follow-up. Data from large-scale trials demonstrating high and durable responses and favorable safety have resulted in Glivec being considered as standard frontline therapy for patients with CML. Such trials have not been conducted for imatinib copy drugs. In the absence of clinical trial data, information from individual cases is critical to assessing the utility of copy drugs. This report suggests that initial treatment with an imatinib copy drug may compromise efficacy.