Mobile-Directly Observed Therapy on Adherence to Hydroxyurea

Inclusion Criteria: * Age ≥18 years and living in urban Dar es Salaam * Male or female (post-menopausal, sterile, or using an acceptable method of contraception) * Negative urine pregnancy test at Screening and a negative urine pregnancy test (dipstick) prior to randomization and dosing * Hemoglobin SS genotype * Absolute neutrophil count \>1,500/uL * Platelet count \>95,000/uL * Serum creatinine\< 100 µmol/L (1.2 mg/dL) * Alanine transaminase (ALT) less than two times the upper limit of normal * Being able and willing to record and submit videos electronically Exclusion Criteria: * Chronic transfusion program as defined by participating in a scheduled (pre-planned) series of transfusions for prophylactic purposes or has a hemoglobin A level that is \>20% of the total hemoglobin * Hemoglobin \<4.0 g/dL * HIV positive * Female planning to become pregnant during the study period * Serious mental (including psychosis) or physical illness, which, in the opinion of the Investigators would compromise participation in the study (e.g. impaired mental capacity, alcoholism * Any condition which the Investigators judge to preclude safe participation in the study or to confound the evaluation of the study outcome.