Adherence to deferoxamine (DFO) is vital for the long-term survival of patients with thalassemia; however, currently no measure exists to quantify adherence directly. In this study, 90 patients with thalassemia major underwent liver iron concentration (LIC) assessment by SQUID biosusceptometer, were asked to rate their adherence to DFO using a Numerical Likert Scale (NLS), and were educated about complications of iron overload. Of 38% (n = 28) of patients who rated themselves as very compliant, 19 had elevated LIC related to inadequate dosing of DFO and nine reported nonadherence in the past. Adherence improved after counseling and LIC decreased by 25% (7-60%) in eight previously noncompliant patients who returned for subsequent LIC over 15 months. In conclusion, the NLS seems to be a simple but reliable tool to assess patients' adherence to DFO. Education and frequent noninvasive LIC assessments can improve adherence and iron burden. Elevated LIC does not necessarily reflect concurrent noncompliance; however, it can be an indication of nonadherence in the past.