Although low birthweight represents a significant risk factor for mortality and morbidity in the perinatal and neonatal period, little is known about its long-term influence on mortality and morbidity in later life. Similarly, the relationship between low birth weight and previous adverse pregnancy outcomes in unclear, as is the influence of genetic factors on birthweight. This study is designed to address all three issues by use of record linkage techniques on 1,200,000 individuals born in British Columbia during 1946-1981. Birth records from this cohort will be linked to form approximately 750,000 sibships. These in turn will be linked into about 250,000 extended, three-generational family sets. Mortality data from the same period, along with morbidity data derived from the British Columbia Health Surveillance Registry, and hospital admissions/discharge forms, will then be linked into the database. The database will be subdivided into seven 5-year cohorts and then analyzed. The first objective will be to define the relationship between demographic, genetic (familial) and obstetrical factors and birthweight. These analyses will investigate the relationship between previous adverse pregnancy outcome and birthweight and define the relationship between birthweight and perinatal outcome in parents, siblings, aunts/uncles and cousins. The second objective will be to evaluate whether low birthweight is a significant risk factor for increased mortality or morbidity later in childhood and on into early adulthood. This will be done by estimating the association of low birthweight with i) adverse pregnancy outcome, especially perinatal mortality and congenital malformations ii) with cause-specific mortality up to age 30; iii) with risk of morbidity as measured by number and duration of hospitalisation, along with cause for hospitalisation. Analyses will include proportional hazards models, log-linear models and case-control comparisons using logistic regression.