The objective of this study was to assess the response of subsyndromal separation anxiety (SSSA) symptoms to methylphenidate (MPH) treatment in patients with attention-deficit/hyperactivity disorder (ADHD). A group of patients with ADHD and SSSA (n=42), aged 8–17 years, received 12 weeks of MPH treatment. The severity of SSSA symptoms was assessed using appropriate scales including the Screen for Child Anxiety Related Emotional Disorders and the specially designed Child and Adolescent Separation Anxiety Scale (CASAS). The severity of ADHD symptoms was assessed using the ADHD Rating Scale. The severity of ADHD and separation anxiety reduced significantly and significant positive correlations were found between the changes in ADHD Rating Scale and the total CASAS scores (P=0.012), as well as other relevant subscales of Screen for Child Anxiety Related Emotional Disorders and CASAS. The MPH-related attenuation in the severity of ADHD was associated with a corresponding improvement in separation anxiety related to school. SSSA symptomatology may be secondary to ADHD and thus the alleviation in ADHD symptoms achieved by MPH treatment results in corresponding relief in separation anxiety.