During pregnancy and in the year after birth women can be affected by a range of mental health problems, including anxiety, depression and postnatal psychotic disorders. These are collectively called perinatal mental illnesses. Perinatal mental illnesses affect at least 10% of women and, if untreated, can have a devastating impact on them and their families. When mothers suffer from these illnesses it increases the likelihood that children will experience behavioural, social or learning difficulties and fail to fulfil their potential. Effective prevention, detection and treatment of perinatal mental illnesses could have a positive impact on the lives of tens of thousands of families and improve the wellbeing, health and achievement of children across the country. If we are to significantly reduce the harm caused by perinatal mental illnesses, a significant change is needed in our universal services so that health professionals are confident in detecting, discussing and dealing with mental illnesses. Mental health needs to be given parity of esteem with physical health in the work of primary care services. Taken together, perinatal depression, anxiety and psychosis carry a total long-term cost to society of about £8.1 billion for each one-year cohort of births in the UK. This is equivalent to a cost of just under £10,000 for every single birth in the country. 72% of this cost relates to adverse impacts on the child rather than the mother. Perinatal mental illnesses are a major public health issue that must be taken seriously. Over a fifth of total costs (£1.7 billion) are borne by the public sector, with the bulk of these falling on the NHS and social services (£1.2 billion).The average cost to society of one case of perinatal depression is around £74,000, of which £23,000 relates to the mother and £51,000 relates to impacts on the child. The current provision of services is widely described as patchy, with significant variations in coverage and quality around the country. For example about half of all cases of perinatal depression and anxiety go undetected and many of those which are detected fail to receive evidence based forms of treatment. These conditions can contribute to women not returning to work following maternity leave and then subsequently finding it much harder to make the step from unemployment into the work place.