Biological risk factors during intra-uterine life, delivery and the neonatal period, and measures of social adversity during pregnancy, were studied as predictors of a 'mildly impaired' (50 to 74) or 'borderline' (75 to 84) score on the Peabody Picture Vocabulary Test (PPVT) at aged five years in 3906 children. Biological risk factors in pregnancy were associated with neither PPVT outcome. Gestation of < 36 weeks, > 3 minutes to establishment of respiration and admission to intensive care were associated with a lower PPVT score indicating mild impairment, though only in the unadjusted analyses. A five minute Apgar score of < 5 and male sex were related to borderline scores, though only the latter remained significant after statistical allowance for possible confounding. In contrast, almost all measures of social adversity were related to both PPVT outcomes even after statistical adjustment for the influence of other factors.