The aim of this study was to investigate the relative importance of perinatal, social, and environmental factors in a birth cohort for the risk of developing asthma in a 10-year follow-up. A group of children (n = 144) with medically diagnosed asthma was matched to a control group of demographic twins (n = 144) from the same birth cohort and region. In a defined region in Sweden, children with a well-documented and medically confirmed asthma diagnosis were retrospectively identified and followed from birth up to the age of 10. Asthma diagnosis, perinatal and obstetric factors, and social data for both the case and control groups were collected through medical records at all health centers in primary care, privately practicing pediatricians, and the public pediatric clinic in the region. The parents of these children answered the standardized ISAAC postal questionnaire, with an overall response rate of 87%. Family history of asthma and allergic rhinitis and low birth weight indicated an increased asthma risk. The social class of the mother and life-style factors concerning mothers smoking habits and indication of passive smoking were also related to increased asthma risk. Also residential factors like mist or mold damage, unusual odors, and dry air were found to indicate increased asthma risk. Maternal asthma, low birth weight, and exposure to passive smoking in the family were all found to be independent predictors for childhood asthma.