Youth diagnosed with sickle cell disease (SCD) may have difficulty taking medication as prescribed (adherence). Hydroxyurea (HU) is one medication that youth may take to help manage SCD. Electronic adherence monitoring is widely considered the gold standard in objective adherence measurement. These monitors provide continuous, real-time records of medication adherence and reveal problematic behavior patterns, including underdosing, overdosing, delayed dosing, "drug holidays" (i.e. where individuals do not take medications for a specified interval of time), and "white coat" adherence (i.e., a pattern of drug adherence as a function of time where individuals display good adherence immediately before and after clinic attendance with worsening adherence in the period between).