Motor and postural behavior in the supine position was studied in 22 low-risk, preterm infants by serial video-recordings from 30-33 to 46-54 weeks' postmenstrual age. Head posture at rest changed from head-to-side to head-in-midline; head movements changed in type and became more frequent; asymmetrical tonic neck posture, occasional until 43-45 weeks, nearly disappeared at 46-54 weeks. Increasing hip inward rotation from the initial flat position and shoulder lifting from the mattress were observed; signs pointing to loss of balance during movement and postures possibly counteracting loss of balance were observed in a large number of the preterm infants until 43-45 weeks. Limb body-oriented posture and movements appeared from term age onwards. Interindividual variability in timing and development of motor and postural items was found. These findings indicate early maturation of postural behavior; they may be relevant to the assessment of postural development of low- and high-risk preterm infants.