INTRODUCTION Women in the UK are having children at increasingly older ages. Older mothers are more likely to have medical co-morbidities and suffer from complications in pregnancy and during delivery. METHODS Routine data on all singleton births at St Thomas' Hospital between 2004 and 2012 was extracted and analysed using logistic regression. Adverse obstetric outcomes were stillbirth, emergency caesarean section, instrumental delivery, postpartum haemorrhage, pre-term birth and pre-eclampsia. Adverse neonatal outcomes were neonatal death, low birth weight and admission to neonatal intensive care. Adjusted odds ratios were used to calculate population attributable fractions (PAF) for maternal age groups. RESULTS There were 47951 singleton births in the study period for which maternal age was known. The mean age at delivery was 31.1 years. 40% of births were associated with an adverse obstetric outcome and 9% with an adverse neonatal outcome. Women aged 30-34 had 27% higher odds (OR 1.27 95% CI 1.19-1.34) of an obstetric event compared to 25-29 year olds having adjusted for parity, ethnicity, BMI, maternal co-morbidities and deprivation, while women aged 40 and older had 61% higher odds (OR 1.61 95% CI 1.46-1.78). Mothers over the age of 40 account for only 2% of 'excess' obstetric risk in this population (PAF 2.4%). CONCLUSION While women of extremely advanced maternal age face the highest risk as individuals, prevention of maternal and neonatal morbidity requires recognition that the highest proportion of maternal age-related obstetric events occur in women aged 30-39.