Stockholm Neonatal Project is a longitudinal population-based study of children born prematurely in 1988-93, with a very low birth weight (&lt;1500 g), who have been followed prospectively from birth through adolescence. A matched control group was recruited at age 5 ½ years. The overall aim was to investigate long-term developmental outcome, paying particular attention to executive functions (EF) in relation to degree of prematurity, birth weight and medical risks. Study I showed a disadvantage in visuo-motor development at 5 ½ years, especially among the preterm boys. Visuo-motor skills were highly related to IQ, and also to EF. In Study II, neuropsychological profiles typical of preterm children and term born children, respectively, were identified through cluster analysis. The general level of performance corresponded well with IQ, motor functions and parental education in both groups, but preterm children had overall lower results and exhibited greater variability across domains. Study III showed that extremely preterm birth (w. 23-27) per se poses a risk for cognitive outcome at age 18, particularly for EF, and that perinatal medical complications add to the risk. By contrast, adolescents born very preterm (w. 28-31) performed just as well as term-born controls in all cognitive domains. However, adolescents born moderately preterm (w. 32-36) and small for gestational age showed general cognitive deficits. Study IV found that cognitive development was stable over time, with parental education and EF at 5 ½ years as significant predictors for cognitive outcome at age 18. Among preterm children, perinatal medical risks and being small for gestational age had a continued negative impact on cognitive development from 5 ½ to 18 years. Study V demonstrated that neuropsychological scoring of Bender drawings, developed in study I, predicted cognitive outcome in adolescence, indicating that the method  may be useful in developmental screening around school entry. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Submitted.</p>