The consistent presence of an abnormal quality of general movements (GMs) during the first postnatal months points to a high risk for the development of a neurological disability. To elucidate the significance of abnormal GMs during a single assessment, a classification system for abnormal GMs was developed. To this end six term and ten preterm infants with abnormal GMs were studied longitudinally with video and electromyographic (EMG) recordings till 59 weeks postmenstrual age (PMA). Two basic categories of abnormal GMs were distinguished: (1) mildly abnormal GMs (two types), which lacked fluency while conserving pattern complexity, and (2) definitely abnormal GMs (four types), which lacked fluency and complexity altogether. GM type before 39 weeks PMA correlated with findings on neonatal ultrasound brain scans. GM quality after 47 weeks PMA was strongly related to neurodevelopmental outcome at 1 1/2 years of age, suggesting that the absence of the age-specific 'fidgety' character of GMs could be a herald of disability.