We report a 44-year-old female patient with attention deficit hyperactivity disorder (ADHD), combined subtype (DSM-IV: 314.01), who was treated with 0.5 mg of short-acting immediate-release methylphenidate/kg body weight given t.i.d. (total daily MPH IR dosage 45 mg). Under this medication, the patient reported significant reduction of symptoms. However, several times a day she experienced severe rebound phenomena with pronounced concentration disturbances, unrest, and dysphoric mood. After changing the medication to long-acting methylphenidate once daily (total daily OROS MPH dosage 54 mg), the rebound phenomena stopped, with equivalent beneficial clinical effects.