Postpartum anxiety and depression is a major public health concern because of its adverse effects on the cognitive and social development of the infant. Globally postpartum depression has been widely investigated but as anxiety is a more prominent feature of postpartum depression we assessed the prevalence of anxiety and depression and their associated factors in post partum women. A quasi-experimental study investigating the impact of postpartum anxiety and depression on child growth and development was conducted in two peri-urban, multiethnic, communities of Karachi, a mega city of Pakistan. A house to house questionnaire based survey was done by trained field workers; 420 consenting pregnant women were identified and data for socio-demographic, home environment and family relationship variables was collected between 36 weeks of pregnancy and within 10 days of childbirth. Mother's levels of anxiety and depression were assessed after one month, two months, six months and twelve months of childbirth; this was two step process: initially an indigenous, validated screening instrument Aga Khan University Anxiety and Depression Scale was used and diagnostic confirmation was done through a psychologist's interview based on DSM IV criteria. Women found to be anxious and depressed at least once out of four assessments were considered for the computation of overall prevalence of postpartum anxiety and depression as well as its risk factors. However, point prevalence's of postpartum anxiety and depression were also reported at each assessment time. Two sixty seven women could be followed for one year. Data was analyzed using SPSS. Chi-square test, simple and multiple logistic regression were used to see the association of different factors. The overall prevalence of postpartum anxiety and depression was found to be 28.8 percent. Domestic violence, difficulty in breast feeding at birth and unplanned current pregnancy were found to be significantly associated with postpartum anxiety and depression. Domestic violence and not having the right to plan pregnancy are related to the patriarchal culture and lack of empowerment of women. The association with difficulties in breast feeding needs to be further explored in future studies.