Difficulties in sustaining posture can present with features associated with hyperactive behaviour listed in DSM-5 and ICD-10 classifications for ADHD. Information from a system measuring motor activity during a neurocognitive test (QbTest), occupational therapist reports and Conners rating scales are compared between cases with and without posture problems. Weakness in sustaining posture results in elevated activity measures during infrared motion analysis. Strong posture on the other hand appears to mitigate activity levels. Posture is an independent factor which requires consideration during the assessment of ADHD.