To systematically examine gross motor development in the first 18 months of life of preterm infants. A total of 800 preterm infants (356 boys), ages between 1 and 18 months and corrected for degree of prematurity, were assessed with the use of the Alberta Infant Motor Scale. Comparison of the mean Alberta Infant Motor Scale scores of the preterm infants with the norm-referenced values derived from term infants revealed that as a group, the preterm infants scored significantly lower at all age levels, even with full correction for degree of prematurity. In general, preterm infants exhibit different gross motor developmental trajectories compared with term infants in the first 18 months of life. The gross motor developmental profile of preterm infants may reflect a variant of typical gross motor development, which seems most likely to be specific for this population. As a consequence, adjusted norms should be used for proper evaluation and clinical decision-making in relation to preterm infants.