Flensborg-Madsen T, et al. - Mothers of 4,009 children from the Copenhagen Perinatal Cohort (1959–61) were questioned by a physician about 20 developmental milestones at a three-year investigation in order to do a systematic assessment of a broad range of potential predictors of milestone accomplishment during the second and third years to recognize factors that describe important inter-individual variation. By perinatal and early postnatal factors, an important amount of variety in the timing of milestones during the first three years of life could be described. The study gave evidence that developmental continuity was the chief predictor of milestones in the second and the speed of development during the first year was third years.