The optimality concept of Prechtl was adopted for the investigation of a series of 229 newborn infants, selected by paired sampling as controls to 116 dyskinetic cerebral palsy cases. A list of 34 conditions, subgrouped into 14 prepartum, 10 partum and 10 postpartum items, was designed and criterias for optimality were defined. When a condition fell short of criteria for optimality, the infant concerned was given a non-optimal point. The sum of non-optimal points for each infant was defined as the reduced optimality score and the proportion of non-optimal points as the reduced optimality rate. The self-weighting capacity of the reduced optimality score system was confirmed. Lack of optimality compared to optimality in a particular item was generally related to a significant increase of the reduced optimality rates of remaining items. Reduced optimality compared to optimality was in the prepartum period significantly more often followed by reduced optimality than optimality in the partum and postpartum periods. In clinical categories - preterm birth, low birth weight, small for gestational age, and combinations of these - a significant increase of the reduced optimality rates were found. Outcome in items comparable to vital statistics were all close to the expected. The series was considered representative for Swedish children born during the period from 1959-70.