Pregnancy and childbirth are often perceived as happy occasions but they may sometimes turn into a distressing experience. During this period, some mental illnesses may start or the existing illnesses may deteriorate. Unfortunately, mothers’ mental health does not receive as much care and attention as their physical health, or diagnosis and treatment of psychological problems are delayed. An untreated mental illness during this period can have negative consequences for both the mother and the developing baby. Decreased self-care of mother can lead to conditions that negatively affect the course of pregnancy, such as weight loss, irregular nutrition, and the onset of diabetes. As for the baby, some of the problems which may be witnessed are low birth weight, premature birth, inadequacy in the development of the nervous system, and negative affect on emotional and behavioral development. In the postpartum period, mother with a mental illness in the postpartum period cannot display sufficient care and attention towards her baby and this may adversely affect mother-child attachment. The most common psychiatric disorder in this period is depression which is diagnosed in every 5-7 mothers. In addition to depression, anxiety disorders, mood disorders and psychosis are mental illnesses that may be diagnosed during this period. This article aims to draw attention to the importance of diagnosis and treatment of mental diseases and their implications for child mental health by informing about mental illnesses that the mother may suffer during pregnancy and postnatal period.