Periventricular flaring (PVF) or periventricular leukomalacia (PVL) was diagnosed by brain ultrasound during the neonatal period in 44 infants (34 males, 10 females; mean gestational age 31 weeks 2 days, SD 2 weeks 1 day) admitted between 1995 and 1997. The infants were divided into three groups according to the severity of their condition. At 0, 3, and 6 months' corrected age an age-adequate neurological examination with special emphasis on the relation between active and passive muscle power was performed and symmetry between right and left sides was assessed. Results for the whole body, as well as for the shoulders, trunk, and legs were classified as optimal, suspect, or abnormal. Motor outcome at 18 months' corrected age was graded in the same way. An overall optimal muscle power regulation was found in one infant at 0, two at 3, and one at 6 months. Suspect outcome was found at all ages in the three groups. At 0 months muscle power regulation did not differ between the three groups. At 3 and 6 months overall poor muscle power, primarily caused by poor muscle power regulation in the shoulders and trunk, was found in infants with PVL grades III or IV. At 18 months' corrected age 24 infants showed no neurological impairment, eight infants had minor impairment, and 12 infants had severe impairment, including all 10 infants categorized as having PVL grades III or IV. The best predictors of impairment at 18 months were the combined results of muscle power in the shoulders and trunk at 3 months with those of the shoulders at 6 months.