We have previously demonstrated an association between neonatal phototherapy and/or neonatal icterus and risk of hospitalization for childhood asthma. This study included children who were prescribed anti-asthmatic medication on a population basis to study exposures during the foetal and neonatal period and risk of childhood asthma. The Swedish Medical Birth Register was linked to the Swedish Prescribed Drug Register. Perinatal data for singleton children who were prescribed anti-asthmatic medication (n = 61,256) were compared with corresponding data for all singleton children born in Sweden from 1 January 1990 to 30 June 2003 and surviving to 1 July 2005 (n = 1,338,319). Mantel-Haenszel's odds ratios were calculated after adjustment for various known confounders. Being the first-born child, maternal age above 44 yr, involuntary childlessness for more than 1 yr, maternal smoking during pregnancy, maternal diabetes mellitus of any kind, pre-eclampsia, caesarean section, and instrumental vaginal delivery were all associated with an increased prescription of anti-asthmatic medication during childhood. Preterm birth, low birth weight, being small for gestational age, respiratory problems, mechanical ventilation, and sepsis and/or pneumonia were also associated with increased drug prescriptions. Neonatal phototherapy and/or icterus were risk determinants for children who developed asthma before the age of 12. After controlling for confounders, the odds ratio for phototherapy and/or icterus remained at 1.30 (95% confidence interval 1.16-1.47). In conclusion, this large population-based study confirms an association between some maternal and perinatal factors and childhood asthma, including neonatal phototherapy and/or icterus.