Jitteriness is a frequent, well-recognized phenomenon in neonates. Its occurrence in early infancy, beyond the neonatal period, is much less documented. Thirty-eight full-term infants who were jittery after 6 weeks of age were followed until the jitteriness disappeared and then reevaluated at the age of 3 years. The jittery movements had already been observed during the neonatal period in 16 babies but not before 6 weeks of age in 22. In 34 infants (89%), 1- and 5-minute Apgar scores were 9 or 10. At the initial examination, a mildly increased muscle tone was found in 12 infants, and hyperactive deep-tendon reflexes were found in 19. The jitteriness resolved at a mean age of 7.2 +/- 3.4 months. At 3 years, 92% of the infants had a normal neurodevelopmental examination, while in the rest only minor, transient disturbances were found. This study indicates that jitteriness as a sole presentation in infants beyond the neonatal period is a benign phenomenon, associated with an excellent prognosis. Its etiology is unknown but seems most likely to be related to a maturational process within the central nervous system.